THOMAS    A.     EDISON, 

Inventor  of  Telegraphic  Appliances,  Phonograph, 
Incandescent  Lamp,  and  Many  Other  Electrical  Devices 


Power  Stations 

and 

Power  Transmission 


A  Manual  of 

APPROVED    AMERICAN    PRACTICE     IN     THE    CONSTRUCTION,     EQUIPMENT, 
AND    MANAGEMENT     OF     ELECTRICAL    GENERATING    STATIONS, 
SUBSTATIONS,        AND       TRANSMISSION       LINES,       FOR 
POWER,      LIGHTING,     TRACTION,     ELECTRO- 
CHEMICAL,   AND     DOMESTIC     USES 


PART    I— POWER   STATIONS 
PART  II— POWER   TRANSMISSION 


By  GEORGE  C.  SHAAD,   E.E 

Assistant  Professor  of  Electrical  Engineering,  Massachusetts 
Institute  of  Technology 


ILLUSTRATED 


CHICAGO 

AMERICAN   SCHOOL  OF    CORRESPONDENCE 
M  1908     '"* 


f\s 


GENERAL 


COPYRIGHT  1907  BY 
AMERICAN  SCHOOL  OF  CORRESPONDENCE 


Entered  at  Stationers'  Hall,  London 
All  Rights  Reserved 


Foreword 


N  recent  years,  such  marvelous  advances  have  been 
made  in  the  engineering  and  scientific  fields,  and 
so  rapid  has  been  the  evolution  of  mechanical  and 
constructive  processes  and  methods,  that  a  distinct 
need  has  been  created  for  a  series  of  practical 
working  guides,  of  convenient  size  and  low  cost,  embodying  the 
accumulated  results  of  experience  and  the  most  approved  modern 
practice  along  a  great  variety  of  lines.  To  fill  this  acknowledged 
need,  is  the  special  purpose  of  the  series  of  handbooks  to  which 
this  volume  belongs. 

C,  In  the  preparation  of  this  series,  it  has  been  the  aim  of  the  pub- 
lishers to  lay  special  stress  on  the  practical  side  of  each  subject, 
as  distinguished  from  mere  theoretical  or  academic  discussion. 
Each  volume  is  written  by  a  well-known  expert  of  acknowledged 
authority  in  his  special  line,  and  is  based  on  a  most  careful  study 
of  practical  needs  and  up-to-date  methods  as  developed  under  the 
conditions  of  actual  practice  in  the  field,  the  shop,  the  mill,  the 
power  house,  the  drafting  room,  the  engine  room,  etc. 

C,  These  volumes  are  especially  adapted  for  purposes  of  self- 
instruction  and  home  study.  The  utmost  care  has  been  used  to 
bring  the  treatment  of  each  subject  within  the  range  of  the  com- 

17976G 


mon  -understanding,  so  that  the  work  will  appeal  not  only  to  the 
technically  trained  expert,  but  also  to  the  beginner  and  the> self- 
taught  practical  man  who  wishes  to  keep  abreast  of  modern 
progress.  The  language  is  simple  and  clear;  heavy  technical  terms 
and  the  formulae  of  the  higher  mathematics  have  been  avoided, 
yet  without  sacrificing  any  of  the  requirements  of  practical 
instruction;  the  arrangement  of  matter  is  such  as  to  carry  the 
reader  along  by  easy  steps  to  complete  mastery  of  each  subject; 
frequent  examples  for  practice  are  given,  to  enable  the  reader  to 
test  his  knowledge  and  make  it  a  permanent  possession;  and  the 
illustrations  are  selected  with  the  greatest  care  to  supplement  and 
make  clear  the  references  in  the  text. 

C,  The  method  adopted  in  the  preparation  of  these  volumes  is  that 
which  the  American  School  of  Correspondence  has  developed  and 
employed  so*  successfully  for  many  years.  It  is  not  an  experiment, 
but  has  stood  the  severest  of  all  tests — that  of  practical  use — which 
has  demonstrated  it  to  be  the  best  method  yet  devised  for  the 
education  of  the  busy  working  man, 

C.  For  purposes  of  ready  reference  and  timely  information  when 
needed,  it  is  believed  that  this  series  of  handbooks  will  be  found  to 
meet  every  requirement. 


Table    of    Contents 


PART  I— POWER   STATIONS 
LOCATION  OF  STATION  AND  SELECTION  OF  SYSTEM  '  .       ...    Page   3 

Choosing  Site — Provision  for  Future  Extensions — Cost  of  Real  Estate 
— Location  of  Substation — Factors  Determining  Choice  of  Generating 
and  Transmission  Systems — Advantages  of  Concentrating  the  Gener- 
ating Plant — Size  of  Plant. 

STEAM  AND  HYDRAULIC  PLANTS Page  10 

Boiler  Requirements — Types  of  Boilers — Steam  Piping — Interchange- 
ability  of  Units — Size,  Location,  etc.,  of  Pipes — Loss  of  Pressure — • 
Superheating — Feed-Water  and  Feeding  Appliances — Scale  and  Other 
Impurities — Feed-Pumps  and  Injectors — Furnaces — Natural  and  Me- 
chanical Draft — Firing  of  Boilers— Steam  Engines — Steam  Turbines — 
Use  of  Water-Power — Water  Turbines  (Reaction  and  Impulse  Types) 
— Pelton  Wheel — Water-Pressure — Hydraulic  Pipe  Data — Head  and 
Horse-Power — Governors — Gas  Engines  as  Prime  Movers. 

ELECTRICAL  EQUIPMENT  OF  STATIONS Page  36 

Generators  (Direct-Current,  Alternating-Current,  Single-Phase,  Poly- 
phase, Double-Current) — Exciters — Transformers — Storage  Batteries 
— Switchboards  and  Connections — Standard  Wire  and  Cable — Panels — • 
— Ammeters — 'Voltmeters— Rheostats  —  Circuit-Breakers — Bus-Bars — 
Oil  Switches — Tripping  Magnets — Lightning  Arresters — Reverse-Cur- 
rent Relays — Speed-Limit  Devices — Substations. 

STATION  BUILDINGS,  RECORDS,  AND  OFFICE  MANAGEMENT  .       .    Page  63 

Layout  of  Structure  and  Appointments — Station  Records — Operating 
Expenses — Fixed  Charges — Depreciation — Methods  of  Charging. 

\ 

PART  II— POWER  TRANSMISSION 
CONDUCTORS Page   1 

Materials  Used  —  Temperature  Coefficient  —  Weight  —  Mechanical 
Strength — Effects  of  Resistance — Current-Carrying  Capacity — Insulat- 
ing Covering  for  Wires — Annunciator  Wire — Underwriter's  Wire — 
Weatherproof  Wire — Gutta-Percha  and  India  Rubber. 

DISTRIBUTION  SYSTEMS  AND  TRANSMISSION  LINES.       .       .       .    Page  11 

Series  Systems — Parallel  or  Multiple-Arc  Systems — Feeders  and  Mains 
— Parallel  and  Anti-Parallel  Feeding — Series-Multiple  and  Multiple- 
Series  Systems — Multiple-Wire  Systems — Voltage  Regulation  of  Par- 
allel Systems — Alternating-Current  Systems  (Series,  Parallel) — 
Polyphase  Systems^  (Two-Phase,  Three-Phase)' — Calculation  of  A.  C. 
Lines — Wiring  Formulae — Transformers — Losses — Efficiency — Regula- 
tion— Overhead  Lines — Poles — Guying — Cross- Arms — Insulators — Pins 
— Temperature  Effects — Underground  Construction — Vitrified  Con- 
duit— Fibre  Conduit — Manholes — Cables — Protection  of  Circuit. 

INDEX  .       . Page  75 


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POWER  STATIONS, 


With  the  rapid  increase  of  the  use  of  electricity  for  power, 
lighting,  traction,  and  electro- chemical  processes,  the  powerhouses 
equipped  for  the  generation  of  the  electrical  supply  have  increased 
in  size  from  plants  containing  a  few  low-capacity  dynamos,  belted 
to  their  prime  movers  and  lighting  a  limited  district,  to  the  mod- 
ern central  station,  furnishing  power  to  immense  systems  and  over 
extended  areas.  Examples  of  the  latter  type  of  station  are  found 
at  Niagara  Falls,  such  stations  as  the  Metropolitan  and  Manhattan 
stations  in  New  York  City,  the  plants  of  the  Boston  Edison  Illu- 
minating Company,  etc. 

The  subject  of  the  design,  operation,  and  maintenance  of  cen- 
tral stations  forms  an  extended  and  attractive  branch  of  electrical 
engineering.  The  design  of  a  successful  station  requires  scientific 
training,  extensive  experience,  and  technical  ability.  Knowledge 
of  electrical  subjects  alone  will  not  suffice,  as  civil  and  mechanical 
engineering  ability  is  called  into  play  as  well,  while  ultimate 
success  depends  largely  on  financial  conditions.  Thus,  with  un- 
limited capital,  a  station  of  high  economy  of  operation  may  be 
designed  and  constructed,  but  the  business  may  be  such  that  the 
fixed  charges  for  money  invested  will  more  than  equal  the  differ- 
ence between  the  receipts  of  the  company  and  the  cost  of  the  gen- 
eration of  power  alone.  In  such  cases  it  is  better  to  build  a  cheaper 
station  and  one  not  possessing  such  extremely  high  economy,  but 
on  which  the  fixed  charges  are  so  greatly  reduced  that  it  may  be 
operated  at  a  profit  to  the  owners. 

The  designing  engineer  should  be  thoroughly  familiar  with 
the  nature  and  extent  of  the  demand  for  power  and  with  the  prob- 
able increase  in  this  demand.  Few  systems  can  be  completed  for 
their  ultimate  capacity  at  first  and,  at  the  same  time,  operated 
economically.  Only  such  generating  units,  with  suitable  reserve 
capacity,  as  are  necessary  to  supply  the  demand  should  be  installed 
at  first,  but  all  apparatus  should  be  arranged  in  such  a  manner 
that  future  extensions  can  be  readily  made. 


POWER  STATIONS 


The  subjects  of  power  stations,  as  here  treated,  will  consider 
the  following  general  topics  : 

Location  of  station  and  substation3  with  choice  of  system  to  be  em- 
ployed. 

Steam  plants,  boilers,  piping,  prime  movers,  etc. 

Hydraulic  plants. 

The  use  of  other  prime  movers. 

The  electrical  plant,  generators,  and  exciters,  switching  apparatus,  etc. 

Buildings. 

Station  records,  methods  of  charging  for  power,  etc. 

LOCATION  OF  THE  GENERATING  STATION. 

The  choice  of  a  site  for  the  generating  station  is  very  closely 
connected  with  the  selection  of  the  system  to  be  used,  which  sys- 
tem, in  turn,  depends  largely  on  the  nature  of  the  demand,  so  that 
it  is  a  little  difficult  to  treat  these  topics  separately.  Several  possi- 
ble sites  are  often  available,  and  we  may  either  consider  the  require- 
ments of  an  ideal  location,  selecting  the  available  one  which  is 

ct> 

nearest  to  this  in  its  characteristics,  or  we  may  select  the  best  system 
for  a  given  area  and  assume  that  the  station  may  be  located  where 
it  would  be  best  adapted  to  this  system.  Wherever  the  site  may 
be,  it  is  possible  to  select  an  efficient  system,  though  not  always 
an  ideal  one. 

The  following  points  should  be  considered  in  the  location  of 
a  station,  no  matter  what  the  system  used : 

1.  Accessibility. 

2.  Water  supply. 

3.  Stability  of  foundation. 

4.  Surroundings. 

5.  Facility  for  extension. 

6.  Cost  of  real  estate. 

The  station  should  be  readily  accessible  on  account  of  the 
delivery  of  fuel  and  stores,  and  of  the  machinery,  while  it  should 
be  so  located  that  ashes  and  cinders  may  be  easily  removed.  If 
possible,  the  station  should  be  located  so  as  to  be  reached  by  both 
rail  and  water,  though  the  former  is  generally  more  desirable.  If 
the  coal  can  be  delivered  to  the  bunkers  directly  from  the  cars,  the 
very  important  item  of  the  cost  of  handling  fuel  may  be  greatly 
reduced.  Again,  the  station  should  be  in  such  a  location  that  it 

O  " 

may  be  readily  reached  by  the  workmen. 


POWEK  STATIONS 


Cheap  and  abundant  water  supply  for  Loth  boilers  and  con- 
densers  is  of  utmost  importance  in  locating  a  steam  station.  The 
quality  of  the  water  supply  for  the  boiler  is  of  more  importance 
than  the  quantity.  It  should  be  as  free  as  possible  from  impuri- 
ties which  are  liable  to  corrode  the  boilers,  and  for  this  reason 
water  from  the  town  mains  is  often  used,  even  when  other  water  is 
available,  as  it  is  possible  to  economize  in  the  use  of  water  by  the 
selection  of  proper  condensers.  The  supply  for  condensing  pur- 
poses should  be  abundant,  otherwise  it  is  necessary  to  install  ex- 
tensive cooling  apparatus  which  is  costly  and  occupies  much 
space. 

The  machinery,  as  -well  as  the  buildings,  must  have  stable 
foundations,  and  it  is  well  to  investigate  the  availability  of  such 
foundations  when  selecting  the  site. 

In  the  operation  of  a  power  plant  using  coal  or  other  fuels, 
certain  nuisances  arise,  such  as  smoke,  noise,  or  vibration,  etc. 
For  this  reason  it  is  preferable  to  locate  where  there  is  little  lia- 
bility to  complaint  on  account  of  these  causes,  as  some  of  these 
nuisances  are  costly  and  difficult  or  even  impossible  to  prevent. 

A  station  should  be  located  where  there  are  ample  facilities 
for  extension  and,  while  it  may  not  always  be  advisable  to  pur- 
chase land  sufficient  for  these  extensions  at  first,  if  there  is  the 
slightest  doubt  in  regard  to  being  able  to  purchase  it  later,  it 
should  be  bought  at  once,  as  the  station  should  be  as  free  as  possi- 
ble from  risk  of  interruption  of  its  plans.  Often  real  estate  is  too 
high  for  purchasing  a  site  in  the  best  location,  and  then  the  next 
best  point  must  be  selected.  A  consideration  of  all  the  factors 
involved  is  necessary  in  determining  whether  or  not  this  cost  is 
too  high.  In  densely  populated  districts  it  is  necessary  to  econo- 
mize greatly  with  the  space  available,  but  it  is  generally  desirable 
that  the.  machinery  may  all  be  placed  on  the  ground  floor  and  that 
adequate  provision  may  be  made  for  the  storage  of  fuel,  etc. 

The  location  of  substations  is  usually  fixed  by  other  con- 
ditions than  those  which  determine  the  site  of  the  main  power 
house.  Since,  in  the  simple  rotary  converter  substation,  neither 
fuel  or  water  are  necessary  and  there  is  little  noise  or  vibration,  it 
may  be  located  wherever  the  cost  of  real  estate  will  permit,  pro- 
vided suitable  foundation  may  be  constructed.  The  distance 


POWER  STATIONS 


between  substations  depends  entirely  on  the  selection  of  the  sys- 
tem and  the  nature  of  the  service. 

Where  low  voltages  are  used  it  is  essential  that  the  station 
be  located  as  near  the  center  of  the  system  as  possible.  This  cen- 
ter is  located  as  follows: 

Having  determined  the  probable  loads  and  their  points  of 
application  for  the  proposed  system,  these  loads  are  indicated  on  a 
drawing  with  the  location  of  the  same  shown  to  scale.  The  center 
of  gravity  of  this  system,  considering  each  load  as  a  weight,  is 
then  found  and  its  location  is  the  ideal  location,  as  regards  amount 
of  copper  necessary  for  the  distributing  system. 

Consider  Fig.  1,  which  shows  the  location  of  five  different 
loads,  which  in  this  case  are  indicated  by  number  of  amperes. 
Combining  loads  A  and  B,  we  have  Ax  =  By.  x  -f  y  —  a.  Solv- 
ing these  equations  we  find  that 

,,*---- -3^" *B4  A  and  B  may  be  considered  as 

*•  C-*--*"*"" """  f 

a  load  of  A  +  B  amperes  at  F. 

,<H9  Similarly,  C  and  D,  E  and  F, 

/       NXN                           /*C3  and  G  and  II  may  be  combined 

SN^IS               /  giying  us   I>   the  center  of  the 

/                          NSN         /  system.     The  amount  of  copper 

/3                                 Nxyo9  necessary  for  a  given  regulation 

/  runs  up  very  rapidly  as  the  dis- 

/  tance  of  the   station    from  this 

D6 

point  increases. 

Selection  of  System.  Gen- 
eral rules  only  can  be  stated  for  the  selection  of  a  system  to  be 
used  in  any  given  territory  for  a  certain  class  of  service. 

For  an  area  not  over  two  miles  square  and  a  site  reasonably 
near  the  center,  for  lighting  and  ordinary  power  purposes,  direct- 
current,  low-pressure,  three-wire  systems  may  be  used.  Either  220 
or  440  volts  may  be  used  as  a  maximum  voltage,  and  motors  should, 
preferably,  be  connected  across  the  outside  wires  of  the  circuits. 
Five-wire- systems  with  440  volts  maximum  potential  have  been 
used,  but  they  require  very  careful  balancing  of  the  load  if  the 
service  is  to  be  satisfactory.  220-volt  lamps  are  giving  good  satis- 
faction; moderate-size,  direct-current  motors  may  be  readily  built 
for  this  pressure  and  constant-potential  arc  lamps  may  be  operated 


POWER  STATIONS 


on  this  voltage  though  not  BO  economically  as  on  110  volts,  if 
single  lamps  are  used.  For  direct-current  railway  work,  the  limit 
of  the  distance  to  which  power  may  be  economically  delivered  with 
an  initial  pressure  of  GOO  volts  is  from  live  to  seven  miles,  depend- 
ing on  the  traffic. 

If  the  area  to  be  served  is  materially  larger  than  the  above, 
or  distances  for  direct-current  railways  greater,  either  of  two  dif- 
ferent schemes  may  be  adopted.  Several  stations  may  be  located 
in  the  territory  and  operated  separately  or  in  multiple  on  the  va- 
rious loads,  or  one  large  power  house  may  be  erected  and  the  en- 
ergy transmitted  from  this  station  at  a  high  voltage  to  various 
transformers  or  transformer  substations  which,  in  turn,  transform 
the  voltage  to  one  suitable  for  the  receivers.  Local  conditions 
usually  determine  which  of  these  two  shall  be  used. 
;:_,  .  The  use  of  several  .low- tension  stations  operating  in  multiple 
is  recommended  only  under  certain  conditions,  namely,  that  the 
demand  is  very  heavy  and  fairly  uniformly  distributed  throughout 
the  area,  and  suitable  sites  for  the  power  house  can  be  readily  ob- 
tained. Such  conditions  rarely  exist  and  it  is  a  question  whether 
or  not  the  single  station  would  not  be  just  as  suitable  for  such 
cases  as  where  the  load  is  not  BO  congested. 

One  reason  why  a  large  central  station  is  preferred  to  several 
smaller  stations  is  that  large  stations  can  be  operated  more  eco- 
nomically, owing  to  the  fact  that  large  units  may  be  used  and  they 
can  be  run  more  nearly  at  full  load.  There  is  a  gain  in  the  cost 
of  attendance,  and  labor-saving  devices  can  be  more  profitably  in- 
stalled. The  location  of  the  power  plant  is  not  determined  to  such 
a  large  extent  by  the  position  of  the  load,  but  other  conditions, 
such  as  water  supply,  cheap  real  estate,  etc.,  will  be  the  governing 
factors.  In  several  cities,  notably  Xew  York  and  Boston,  large 
central  stations  are  being  installed  to  take  the  place  of  several  sep- 
arate stations,  the  old  stations  being  changed  from  generating 
power  houses  to  rotary- converter  substations.  Both  direct-cur- 
rent low-tension  machines,  to  supply  the  neighboring"  districts, 
and  high-tension  alternating-current,  for  supplying  the  outlying 
or  residence  districts,  are  often  installed  in  the  one  station 

As  examples  of  the  central  station  being  located  at  some  dis- 
tance from  the  center  of  the  load,  we  have  nearly  all  of  the  large 


POWER  STATIONS 


hydraulic  power  developments.  Here  it  is  the  cheapness  of  the 
water  power  which  determines  the  power  house  location.  The 
greatest  distance  over  which  powrer  is  transmitted  electrically  at 
present  is  in  the  neighborhood  of  200  miles. 

If  a  high-tension  alternating-current  system  is  to  be  installed, 
there  remains  the  choice  of  a  polyphase  or  single-phase  machine  as 
well  as  the  selection  of  voltage  for  transmission  purposes.  As 
pointed  out  in  "  Power  Transmission  ",  polyphase  generators  are 
cheaper  than  single-phase  generators  and,  if  necessary,  they  can  be 
loaded  to  about  80%  of  their  normal  capacity,  single-phase,  while 
motors  can  be  more  readily  operated  from  polyphase  circuits.  If 
synchronous  motors  or  rotary  converters  are  to  be  installed,  a  poly- 
phase system  is  necessary.  'The  voltage  will  be  determined  by  the 
distance  of  transmission,  care  being  taken  to  select  a  value  consid- 
ered as  standard,  if  possible.  Generators  are  wound  giving  a  volt- 
age at  the  terminals  as  high  as  15,000  volts,  but  in  many  districts 
it  is  desirable  to  use  step-up  transformers  for  voltages  above  6,600 
on  account  of  liability  to  troubles  from  lightning. 

With  the  development  of  the  single-phase  railway  motor,  cen- 
tral stations  generating  single-phase  current  only,  will  be  built  in 
larger  sizes  than  previously,  as  their  use  heretofore  has  been  lim- 
ited to  lighting  stations. 

Size  of  Plant.  A  few  general  notes  in  regard  to  the  design 
of  plants  will  be  given  here,  the  several  points  being  taken  up 
more  in  detail  later. 

Direct  driving  of  apparatus  is  always  superior  to  methods  of 
gearing  or  belting  as  it  is  efficient,  safe,  and  reliable,  but  it  is  not  as 
flexible  as  shafting  and  belts,  and  on  this  account  its  adoption  is 
not  universal. 

Speeds  to  be  used  will  depend  on  the  type  and  size  of  the 
generating  unit.  Small  machines  are  always  cheaper  when  run  at 
high  speeds,  but  the  saving  is  less  on  large  generators.  For  large 
engines,  slow  speed  is  alwrays  preferable. 

It  is  desirable  that  there  be  a  demand  for  both  power  and 
lighting,  and  a  station  should  be  constructed  which  will  serve  both 
purposes.  The  use  of  power  will  create  a  day  load  for  a  lighting 
station  which  does  much  to  increase  its  ultimate  efficiency  and,  as 
a  rule,  its  earning  capacity. 


POWER   STATIONS 


In  addition  to  generator  capacity  necessary  to  supply  the  load, 
a  certain  amount  of  reserve,  either  in  the  way  of  additional  units 
or  overload  capacity,  must  be  installed.  The  probable  load  for  say 
three  years  can  be  closely  estimated  and  this,  together  with  the 
proper  reserve,  will  determine  the  size  of  the  station.  The  plaat 
as  a  whole,  including  all  future  extensions,  should  be  planned  at 
the  start  as  extensions  will  then  be  greatly  facilitated.  Usually  it 
will  not  be  desirable  to  begin  extensions  for  at  least  three  years 
after  the  first  part  of  the  plant  has  been  erected. 

Enough  units  must  be  installed  so  that  one  or  more  may  be 
laid  off  for  repairs,  and  there  are  several  arguments  in  favor  of 
making  this  reserve  in  the  way  of  overload  capacity,  for  the  gen- 
erators at  least.  Some  of  these  arguments  are:  .Reserve  is  often 
required  at  short  notice,  notably  in  railway  plants.  With  overload 
capacity,  rapid  increase  of  load,  such  as  occurs  in  lighting  stations 
when  darkness  comes  on  suddenly,  may  be  more  readily  taken  care 
of.  There  is  always  a  factor  of  safety  in  machines  not  •running  to 
their  fullest  capacity.  Reserve  capacity  is  cheaper  in  this  form 
than  if  installed  as  separate  machines.  As  a  disadvantage,  we 
have  a  lower  efficiency,  due  to  machines  not  usually  running  at 
full  load,  but  in  the  case  of  generators  this  is  yery  slight. 

With  an  overload  capacity  of  33  J%,  four  machines  should  be 
the  initial  installment  since  one  can  be  laid  off  for  repairs  if  neces- 
sary, the  total  load  being  readily  carried  by  three  machines.  In 
planning  extensions,  the  fact  that  at  least  one  machine  may  require 
to  be  laid  off  at  any  time  should  not  be  lost  sight  of,  while  the 
units  should  be  made  as  large  as  is  conducive  to  the  best  operation. 

TABLE   1. 
Permissible  Overload  33  per  cent. 


Machines 
one  at  a 

added 
time. 

Machines 
two  at  a 

added 
time. 

Machines 
three  at  i 

added 
i  time. 

Initial  installment. 

t 

Size. 
500 

No.. 
4 

Size. 
500 

No. 
4 

Size. 
500 

First  extension  

1 

666 

2 

1000 

a 

2000 

Second      ' 

1 

888 

2 

2000 

5 

5000 

Third         '         

1 

lias 

2 

4000 

4 

5000 

Fourth      '         

1 

1577 

4 

4000 

Fifth          '         

1 

2103 

8 

4000 

Sixth         '         

1 

2804 

10  POWER   STATIONS 


Table- 1  is  worked  out  showing  the  initial  installment  fora 
2,000-K.AV.  plant  with  future  extensions.  It  is  seen  from  this 
table  that  adding  two  machines  at  a  time  gives  more  uniformity  in 
the  size  of  units — a  very  desirable  feature. 

The  boilers  should  be  of  large  units  for  stations  of  large 
capacity,  while  for  small  stations  they  must  be  selected  so  that  at 
least  one  may  be  laid  off  for  repairs. 

STEAM  PLANT. 
BOILERS. 

The  majority  of  power  stations  have  their  machinery  driven 
by  either  steam  or  water  power,  though  there  are  many  using  gas 
engines  as  prime  movers.  If  a  steam  plant  is  being  considered. 
one  of  the  first  subjects  to  be  taken  up  is  the  generation  of  the 
steam.  The  subject  of  boilers  is  one  of  vital  importance  to  the 
successful  operation  of  steam-driven  central  stations.  The  object 
of  the  boiler  with  its  furnace  is  to  abstract  as  much  heat  as  possi- 
ble from  the  fuel  and  impart  it  to  the  water.  The  various  kinds 
of  boilers  used  for  accomplishing  this  more  or  less  successfully  are 
described  in  books  on  boilers,  and  we  will  consider  here  the  merits 
of  a  few  of  the  types  only  as  regards  central-station  operation. 

The  requirements  are:  First,  that  steam  be  available  through- 
out the  twenty-four  hours;  the  amount  required  at  different  parts 
of  the  day  varying  considerably.  Thus,  in  a  lighting  station,  the 
demand  from  midnight  to  6  a.  in.  is  very  light,  but  toward  eve- 
ning, when  the  load  on  the  station  increases  very  rapidly,  there  is  an 
abrupt  increase  in  the  rate  at  which  steam  must  be  given  off.  The 
maximum  demand  can  be  readily  anticipated  under  normal  weather 
conditions,  but  occasionally  this  maximum  will  be  equaled  or  even 
exceeded  at  unexpected  moments.  For  this  reason  a  certain  num- 
ber of  boilers  must  be  kept  under  steam  constantly,  more  or  less 
of  them  running  with  banked  fires  during  light  loads.  If  the 
boilers  have  a  small  amount  of  radiating  surface,  the  loss  during 
idle  hours  will  be  decreased. 

Second,  the  boilers  must  be  economical  over  a  large  range  of 
rates  of  firing  and  must  be  capable  of  being  forced  without  detri- 
ment. Boilers  should  be  provided  which  work  economically  for  the 
hours  just  preceding  and  following  the  maximum  load  while  they 


POWER  STATIONS       •  11 


may  be  forced,  though  running  at  lower  efficiency,  during  the  peak. 

Thvrd,  coining  to  the  commercial  side  of  the  question,  we  have 
first  cost,  cost  of  maintenance,  and  space  occupied.  The  first  cost, 
as  does  the  cost  of  maintenance,  varies  with  the  type  and  pressure 
of  the  boiler.  The  space  occupied  enters  as  a  factor  only  when 
the  situation  of  the  station  is  such  that  space  is  limited,  or  when  the 
amount  of  steam  piping  becomes  excessive.  In  some  city  plants, 
space  may  be  the  determining  feature  in  the  selection  of  boilers. 

The  Cornish  and  Lancashire  boilers  differ  only  in  the  num- 
ber of  cylindrical  tubes  in  \vhich  furnaces  are  placed.  As  many 
as  three  tubes  are  placed  in  the  largest  sizes  (seldom  used)  of  the 
-Lancashire  boilers.  They  are  made  np  to  200  pounds  steam  pres- 
sure and  possess  the  following  features: 

1.  High  efficiency  at  moderate  rates  of  combustion. 

2.  Low  rate  of  depreciation. 

3.  Large  water  space. 

4.  Easily  cleaned. 

5.  Large  floor  space  required. 

6.  Cannot  be  readily  forced. 

The  Galloway  boiler  differs  from  the  Lancashire  boiler  in  that 
there  are  cross  tubes  in  the  flues. 

In  the  Multitubular  boiler  the  number  of  tubes  is  greatly 
increased  and  their  size  diminished.  Their  heating  surf  ace  is  large 
and  they  steam  rapidly.  They  are  used  extensively  for  power- 
station  work. 

The  chief  characteristics  of  the  water-tube  boilers,  of  which 
there  are  many  types,  are: 

1.  Moderate  floor  space. 

2.  Ability  to  steam  rapidly. 

3.  Good  water  circulation. 

4.  Adapted  to  high  pressure. 

5.  Easily  transported  ami  erected. 

6.  Easily  repaired. 

7.  Not  easily  cleaned. 

8.  Rate  of  deterioration  greater  than  for  Lancashire  boiler. 

9.  Small  water  space,  hence  variation  in  pressure  with  varying 
demands  for  steam. 

10.    Expensive  setting. 

Marine  boilers  require  no  setting.  Among  their  advantages 
and  disadvantages  may  be  mentioned: 


12  POWER   STATIONS 


1.  Exceedingly  small  space  necessary. 

2.  Radiating  surface  reduced. 
8.  Good  economy. 

4.  Heavy  and  difficult  to  repair. 

5.  Unsuitable  for  bad  water. 

6.  Poor  circulation  of  water. 

Another  type  of  boiler,  known  as  the  Economic,  is  a  combi- 
nation of  the  Lancashire  and  multitubular  boilers,  as  is  the  marine 
boiler.  It  is  set  in  brickwork  and  arranged  so  that  the  gases  pass 
under  the  bottom  and  along  the  sides  of  the  boiler  as  well  aa 
through  tne  tubes.  It  may  be  compared  with  other  boilers  from 
the  following  points: 

1.  Small  floor  space. 

2.  Less  radiating  surface  than  the  Lancashire  boiler, 

3.  Not  easily  cleaned. 

4.  Repairs  rather  expensive. 

5.  Requires  considerable  draft.  , 

As  regards  first  cost,  boilers  installed  for  150  pounds  pressure 
and  the  same  rate  of  evaporation,  will  run  in  the  following  order: 
Galloway  and  Marine,  highest  first  cost,  Economic,  Lancashire,  Bab- 
cock  &  Wilcox.  The  Increase  of  cost,  with  increase  of  steam  pres- 
sure, is  greatest  for  the  Economic  and  least  for  the  water-tube  type. 

Deterioration  is  less  with  the  Lancashire  boiler  than  with  the 
other  types. 

The  floor  space  occupied  by  these  various  types  built  for  150 
pounds  pressure  and  7,500  pounds  of  water,  evaporated  per  hour, 
is  given  in  Table  2. 

TABLE  2. 


Kind  of  Boiler. 

Lancashire  ...........................  .............  /  ......  408 

Galloway  .................................................  371 

Babcock  and  Wilcox  .....................................  200 

Marine  wet-back  ..........................................  120 

Economic  .................................................  210 

The  percentage  of  the  heat  of  the  fuel  utilized  by  the  boiler 
is  01  great  importance,  but  it  is  difficult  to  get  reliable  data  in  re- 
gard to  this.  Table  8  is  taken  from  Donkin's  "Heat  Efficiency  of 
Steam  Boilers",  and  will  give  some  idea  of  the  efficiencies  of  the 
different  types.  Economizers  were  not  used  in  any  of  these  tests, 
but  they  should  always  be  used  with  the  Lancashire  type  of  boiler. 


POWER   STATIONS 


13 


TABLE  3. 


Kind  of  Boiler. 

No.  of  Ex- 
periments. 

Mean  Effi- 
ciency of 
two  best 
Experi- 
ments. 

Lowest 
Efficiency. 

Mean   Effi- 
ciency of 
all  Experi- 
ments. 

Lancashire  hand-lired  .            

107 

79.5 

42  1 

62  8 

Lancashire  machine-fired  

40 

78.0 

51  9 

64  2 

Cornish  hand-lired  

25 

81.7 

53.0 

68  0 

Babcock  and  \Vilcox  hand-lired...  . 
Marine  wet-back  hand-lired  
Marine  dry-back  hand-lired  

49 
6 
24 

77.5 
69.6 
75.7 

50.0 
62.0 
64.7 

64.9 
66-0 

69.2 

.  It  is  well  to  select  a  boiler  from  20  to  50  pounds  in  excess  of 
the  pressure  to  be  used,  as  its  life  may  thus  be  considerably  ex- 
tended, while,  when  the  boiler  is  new,  the  safety  valve  need  not 
be  set  so  near  the  normal,  pressure,  and  there  is  less  s.team  wasted 
by  the  blowing  off  of  this  valve.  Again,  a  few  extra  pounds  of 
steam  may  be  carried  just  previous  to  the  time  the  peak  of  the 
load  is  expected.  For  pressures  exceeding  200  or,  possibly,  150 
pounds,  a  water- tube  boiler  should  be  selected. 

In  large  stations,  it  is  preferable  to  make  the  boiler  units  of 
large  capacity,  to  do  away  as  much  as  possible  with  the  extra 
piping  and  fittings  necessary  for  each  unit.  Water-tube  boilers 
are  best  adapted  for  large  sizes.  These  may  be  constructed  for 
150  pounds  pressure,  large  enough  to  evaporate  20,000  pounds  of 
water  per  hour,  at  an  economical  rate. 

To  sum  up — For  stations  of  moderate  size  and  with  medium 
pressures  with  plenty  of  space,  use  Lancashire  or  fire- tube  boilers; 
for  high  pressure  or  large  units,  select  water-tube  boilers;  where 
space  is  limited,  install  marine  boilers,  although  they  are  not  as 
safe  as  water-tube  boilers  for  high  pressures. 

Steam  Piping.  The  piping  from  the  boilers  to  the  engines 
should  be  given  very  careful  consideration.  Sieam  should  be 
available  at  all  times  and  for  all  engines.  Freedom  from  serious 
interruptions  due  to  leaks  or  breaks  in  the  piping  is  brought  about 
by  very  careful  design  and  the  use  of  good  material  in  construction. 
Duplicate  piping  is  used  in  many  instances.  Provision  must 
always  be  made  for  variations  in  length  of  the  pipe  with  variation 
of  temperature.  For  plants  using  steam  at  150  pounds  pressure, 
the  variation  in  the  length  of  steam  pipe  maybe  as  high  as  2.5 


POWER  STATIONS 


inches  for  100  feet,  and  at  least  2  inches  for  100  feet  should  always 
be  counted  upon. 

Arrangement.  Fig.  2  shows  a  simple  diagram  of  the  "  ring" 
system  of  piping.  The  steam  passes  from  the  boiler  by  two  paths 
to  the  engine  and  any  section  of  the  piping  may  be  cut  out  by 


VALISE. 
Fig.  2. 

the  closing  of  two  valves.    Simple  ring  systems  have  the  following 
characteristics:* 

1.  The  range,  as  the  main  pipe  is  called,  must  be  of  uniform  size  and 
large  enough  to  carry  all  of  the  steam  when  generated  at  its  maximum  rate. 

2.  A  damaged  section  may  disable  one  boiler  or  one  engine. 

3.  Several  large  valves  are  required. 

4.  Provision  may  be  readily  made  to  allow  for  expansion  of  pipes. 

Cross  connecting  the  ring  system,  as  showrn  in  Fig.  3,  changes 
these  characteristics  as  follows: 

1.  Size  of  pipes  and  consequent  radiating  surface  is  reduced. 

2.  More  valves  needed  but  they  are  of  smaller  size. 
8.    Less  easy  to  arrange  for  expansion  of  the  pipes. 


POWER   STATIONS 


15 


If  the  system  is  to  be  duplicated,  that  is,  two  complete  sets  of 
main  pipes  and  feeders  installed  .(see  Fig.  4),  two  schemes  are  in  use: 

1.  Each  system  is  designed  to  operate  the  whole  station  at  maxi- 
mum load  with  normal  velocity  and  loss  of  pressure  in  the  pipes,  and  only 
one  system  is  in  use  at  a  time.  This  has  the  disadvantage  that  the  idle 


BO/LZFIS 


Fig.  8. 


section  is  liable  not  to  be  in  good  operating  condition  when  needed.    Large 
pipes  must  be  used  for  each  set  of  mains. 

2.  The  two  systems  may  be  made  large  enough  to  supply  steam  at 
normal  loss  of  pressure  when  both  are  used  at  the  same  time,  while  either 
is  made  large  enough  to  keep  the  station  running  should  the  other  section 
need  repairs.  This  has  the  advantages  of  less  expense,  and  both  sections 
Of  pipe  are  normally  in  use;  but  it  has  the  disadvantages  of  more  radiating 
surface  to  the  pipes  and  consequent  condensation  for  the  same  capacity 
for  furnishing  steam. 


16 


POWER   STATIONS 


Complete  interehangeability  of  units  cannot  be  arranged  for 
if  the  separate  engine  units  exceed  400  to  500  horse  power.  Since 
engine  units  can  be  made  larger  than  boiler  units,  it  becomes  nec- 
essary to  treat  several  boiler  units  as  a  single  unit,  or  battery,  these 
batteries  being  connected  as  the  single  boilers  already  shown.  For 
still  larger  plants  the  steam  piping,  if  arranged  to  supply  any 
engines  from  any  batteries  of  boilers,  would  be  of  enormous  size. 
If  the  boilers  do  not  occupy  a  greater  length  of  floor  space  than 
the  engines,  Fig.  5  shows  a  good  arrangement  of  units.  Any 


Fig.  4. 

engine  can  be  fed  from  either  of  two  batteries  of  boilers  and  the 
liability  of  serious  interruptions  of  service  due  to  steam  pipes  or 
boiler  trouble  is  very  remote. 

Material.  Steel  pipe,  lap  welded  and  fastened  together  by 
means  of  flanges,  is  to  be  recommended  for  all  steam  piping.  TLe 
flanges  may  be  screwed  on  the  ends  of  sections  and  calked  so  as  to 
render  this  connection  steam  tight,  though  in  large  sizes  it  is  better 
to  have  the  flanges  welded  to  the  pipes.  This  latter  construction 


POWER   STATIONS 


17 


costs  no  more  for  large  pipes  and  is  much  more  reliable.  All 
valves  and  fittings  are  made  in  two  grades  or  weights,  one  for  low 
pressures,  and  the  other  for  high  pressures.  The  high -pressure 
fittings  should  always  be  used  for  electrical  stations.  Gate  valves 
should  always  be  selected  and,  in  large  sizes,  they  should  be  pro- 
vided with  a  by-pass. 

Asbestos,  either  alone  or 
with  copper  rings,  vulcan- 
ized india  rubber,  asbestos 
and  india  rubber,  etc.,  are 
used  for  packing  between 
flanges  to  render  them 
steam  tight.  Where  there 
is  much  expansion,  the  ma- 
terial selected  should  be  one 
that  possesses  considerable 
elasticity.  Joints  for  high- 
pressure  systems  require 
much  more  care  than  those 
where  steam  is  used  at  a 
low  pressure,  and  the  num- 
ber of  joints  should  be  re- 
duced to  a  minimum  by- 
using  long  sections  of  pipe. 
A  list  of  the  various  fit- 
tings  required  for  steam 
piping,  together  with  their 
descriptions,  is  given  in 
books  on  boilers.  One  pre- 
caution to  be  taken  is  to 
see  that  such  fittings  do  not 
become  too  numerous  or 
complicated,  and  it  is  well 
not  to  depend  too  much 


Fig.  5. 


on  automatic  fittings.  Steam  separators  should  be  large  enough 
to  serye  as  a  reservoir  of  steam  for  the  engine  and  thus  equalize, 
to  a  certain  extent,  the  velocity  of  flow  of  steam  in  the  pipes. 


18  POWER  STATIONS 


In  providing  for  the  expansion  of  pipes  due  to  change  of 
temperature,  "  IT  "  bends  made  of  steel  pipe  and  having  a  radius 
of  curvature  not  less  than  six  times,  and  preferably  ten  times  the 
diameter  of  the  pipe,  are  preferred.  Copper  pipes  cannot  be  rec- 
ommended for  high  pressures,  while  slip  expansion  joints  are  most 
undesirable  on  account  of  their  liability  to  bind. 

The  size  of  steam  pipes  is  determined  by  the  velocity  of  flow. 
Probably  an  average  velocity  of  60  feet  per  second  would  be  better 
than  100  feet  per  second,  though  in  some  cases  where  space  is 
limited  a  velocity  as  high  as  150  feet  per  second  has  been  used. 

The  loss  in  pressure  in  steam  pipes  may  be  obtained  from  the 
following  formula: 

QVL 

*.-*.*' Tgr 

where    j?,  —  p.2  =  loss  in  pressure  in  pounds  per  sq.  in. 

Q  =  quantity  of  steam  in  cu.  ft.  per  minute. 
d  =  diameter  of  pipe  in  inches. 
.L  =  length  in  feet. 

w  =  weight  per  cu.  ft.  of  steam  at  pressure  JP,. 
c  —  constant  depending  on  size  of  pipe. 

Values  of  c  are  as  follows: 

Diameter  of  pipe..    %"     v'      -"     B"  4"      5"      6"      7"      8"      9"    10" 

Value  of  c 36.8  45.3  52.7  56.1  57.8  58.4  59.5  60.1  60.7  61.2  61.8 

Diameter  of  pipe 12"  14"      16"      18"     20"     22"      24" 

Value  of  c. 62.1  62.3    62.6    62.7    62.9    63.2    63.2 

In  mounting  the  steam  pipe,  it  should  be  fastened  rigidly  at 
one  point,  preferably  near  the  center  of  a  long  section,  and  allowed 
a  slight  motion  longitudinally  at  all  other  supports.  Such  sup- 
ports may  be  provided  with  rollers  to  allow  for  this  motion,  or  the 
pipe  may  be  suspended  from  wrought-iron  rods  which  will  give  a 
flexible  support.  Practice  differs  in  the  location  of  the  steam  pip- 
ing, some  engineers  recommending  that  it  be  placed  underneath 
the  engine  room  floor  and  others  that  it  be  located  high  above  the 
engine  room  floor.  In  any  case  it  should  be  made  easily  access- 
ible, and  the  valves  should  be  located  so  that  nothing  will  inter- 
fere with  their  operation.  Proper  provision  must  be  made  for 
draining  the  pipes. 


PO\YER  STATIONS  1U 


All  piping  &s  well  as  joints  should  be  carefully  covered  with  a 
good  quality  of  lagging  as  the  amount  of  steam  condensed  in  a  bare 
pipe,  especially  if  of  any  great  length,  is  considerable.  In  select- 
ing a  lagging  the  following  points  should  be  noticed.  Covering  for 
steam  pipes  should  be  incombustible,  should  present  a  smooth  sur- 
face, should  not  be  easily  damaged  by  vibration  or  steam,  and 
should  have  as  large  a  resistance  to  the  passage  of  heat  as  possible. 
It  must  not  be  too  thick,  otherwise  the  increased  radiating  surface 

o 

will  counterbalance  the  resistance  to  the  passage  of  heat. 

The  loss  of  power  in  steam  pipes  due  to  radiation  is  given  as 
follows: 


II  =  loss  of  power  in  heat  units. 
(I  —  diameter  of  pipe. 
L  =  length  of  pipe  in  feet. 
r  —  constant  depending  on  steam  pressure  and  pipe  covering. 

Steam  pressure  in  pounds  (absolute)  ......     40  65  90  115 

Values  of  r  for  uncovered  pipe  .............  437  555  620  684 

Value  ofr  for  pipe  covered  with  2  inches  of 

hair  felt  ..............................     48  58  66  73 

Referring  to  table  in  books  on  boilers,  the  relative  values  of 
different  materials  used  for  covering  steam  pipes  may  be  found. 

Superheated  Steam  reduces  condensation  in  the  engines  as 
well  as  in  the  piping?  and  increases  the  efficiency  of  the  system. 
Its  use  was  abandoned  for  several  years,  due  to  difficulties  in 
lubricating  and  packing  the  engine  cylinders,  but  by  the  use  of 
mineral  oils  and  metallic  packing,  these  difficulties  have  been  done 
away  with  to  a  large  extent,  while  steam  turbines  are  especially 
adapted  to  the  use  of  superheated  steam.  The  application  of  heat 
directly  to  steam,  as  is  done  in  the  superheater,  increases  the 
efficiency  of  the  boilers.  Table  4  shows  the  increase  in  boiler 
efficiency  for  a  certain  boiler  test,  the  results  being  given  in 
pounds  of  water  changed  to  dry,  saturated  steam.  Tests  on  vari- 
ous engines  show  a  gain  in  efficiency  as  high  as  9%  with  a  super- 
heat  of  80°  to  100°  F,  while  special  tests  in  some  cases  show  even 
a  greater  gain. 


20 


POWER  STATIONS 


TABLE  4. 


Amount  of  superheat. 

Water  evaporated  per  Ib. 
of  coal. 

Without 
superheat. 

With  super- 
heat. 

40     degrees  F  

7.82 
6.42 
6.00 
6.78 
7.15 

9.99 
7.06 
7.00 
8.66 
8.65 

42           "         ..  

55            " 

56.5        " 

5.5.2        "         ... 

Superheaters  are  very  simple,  consisting  of  tubular  boilers 
containing  steam  instead  of  water,  and  either  located  so  as  to  util- 
ize the  heat  of  the  gases,  the  same  as  economizers,  or  separately 
fired.  They  should  be  arranged  so  that  they  may  be  readily  cut 
out  of  service,  if  necessary,  and  provision  must  be  made  for  either 
flooding  them  or  turning  the  hot  gases  into  a  by-pass,  as  the  tubes 
would  be  injured  by  the  heat  if  they  contained  neither  water  nor 
steam. 

FEED  WATER  AND  FEEDING  APPLIANCES. 

All  water,  such  as  can  be  obtained  for  the  feeding  of  boilers, 
contains  some  impurities,  among  the  most  important  of  which  as 
regards  boilers  are  soluble  salts  of  calcium  and  magnesium.  Bicar- 
bonates  of  the  alkaline  earths  cause  precipitations  on  the  interior 
of  boilers,  forming  "  scale  ".  Sulphate  of  lime  is  also  deposited 
by  concentration  under  pressure.  Scale,  when  formed,  not  only 
decreases  the  efficiency  of  the  boiler  but  also  causes  deterioration, 
for  if  sufficiently  thick,  the  diminished  conducting  power  of  the 
boiler  allows  the  tubes  or  plates  to  be  overheated  .and  to  crack  or 
burst.  Again,  the  scale  may  keep  the  water  from  contact  with 
sections  of  the  heated  plates  for  some  time  and  then,  giving  way, 
large  volumes  of  steam  are  generated  very  quickly  and  an  explo- 
sion may  result. 

Some  processes  to  prevent  the  formation  of  scale  are  used, 
which  affect  the  water  after  it  enters  the  boilers,  but  they  are  not 
to  be  recommended,  and  any  treatment  the  water  receives  should 
affect  it  previous  to  its  being  fed  to  the  boilers.  Carbonates  and 
a  small  quantity  of  sulphate  of  lime  may  be  removed  by  heating 


POWER  STATIONS 


21 


ECONOM/ZERS 


in  a  separate  vessel.     Large  quantities  of  sulphate  of  lime  must 
be  precipitated  chemically. 

Sediment,  small  particles  of  matter  in  suspension,  must  be 
remove*!  by  allowing  the  water  to  settle.  Vegetable  matters  are 
sometimes  present,  which 
cause  a  film  to  be  deposited. 
Certain  gases,  in  solution- 
such  as  oxygen,  nitrogen, 
etc. — cause  pitting  of  the 
boiler.  This  effect  is  neu- 
tralized by  the  addition  of 
chemicals.  Oil,  from  the 
engine  cylinder,  is  particu- 
larly destructive  to  boilers 
and  when  present  in  the 
condensed  steam  must  be 
carefully  removed. 

Both  feed  pumps  and 
injectors  are  used  for  feed- 
ing the  water  to  the  boilers. 
Feed  pumps  may  be  either 
steam  or  motor-driven. 
Steam-driven  pumps  are 
very  inefficient,  but  they  are 
simple  and  the  speed  is  easily 
controlled.  Motor-driven 
pumps  are  more  efficient  and 
neater,  but  more  expensive  and  more  difficult  to  regulate  efficiently 
over  a  wide  range  of  speed.  Direct-acting  pumps  may  have  feed- 
water  heaters  attached  to  them,  thus  increasing  the  efficiency  of 
the  apparatus  as  a  whole.  The  supply  of  electrical  energy  must 
be  constant  if  motor-driven  pumps  are  to  be  used. 

Feed  pipes  must  be  arranged  so  as  to  reduce  the  risk  of  fail- 
ure to  a  minimum,  and  for  this  reason  they  are  almost  always  du- 
plicated. More  than  one  water  supply  is  also  recommended  if  there 
is  the  slightest  danger  of  interruption  on  this  account.  One  com- 
mQn  arrangement  of  feed-water  apparatus  is  to  install  a  few  large 
pumps  supplying  either  of  two  mains  from  which  the  boiler  con- 


Fig.  6. 


22 


POWER  STATIONS 


TABLE   5. 

Giving  Rate  of  Flow  of  Water,  in  Feet  per  Minute,  through  Pipes 
of  Various  Sizes,  for  Varying  Quantities  of  Flow, 


Gallons 
per  Min. 

%  in. 

1  in. 

1%  in 

Itt  in. 

Sin. 

2VS  in. 

3  in. 

4  in. 

5 

218 

122% 

78% 

54% 

30% 

19% 

13% 

'**& 

10 

436 

245 

157 

109 

61 

38 

27 

15 

653 

367% 

235% 

163% 

91% 

58% 

40% 

23  3 

20 

872 

490  " 

314 

218 

122 

78 

54 

30% 

25 

1090 

612% 

392% 

272% 

152% 

97% 

67% 

38% 

30 

735 

451 

327 

183 

117 

81  " 

46 

35 

857% 

549% 

3813^ 

213% 

136% 

94% 

53% 

40 

980 

628  " 

436  " 

244  " 

156  " 

108 

61% 

45 

1102% 

706% 

490% 

274% 

175% 

121% 

69 

50 

785 

545  " 

305 

195 

135 

76% 

75 

1177% 

817% 

457% 

292% 

202% 

115 

100 

1090 

610  " 

380 

270 

153% 

125 

762% 

487% 

337% 

191% 

160 

915 

585 

405 

230 

175 

1067% 

682% 

472% 

268% 

200 

1220  " 

780 

540 

306% 

nections  are  taken.  This  is  a  complicated  and  costly  system  of 
piping.  Fig.  6  shows  a  scheme  used  for  feeding  two  boilers  in 
which  each  pump  is  capable  of  supplying  both  boilers.  Pipes 
should  be  ample  in  cross-section,  and,  in  long  lengths,  allowance 
must  be  made  for  expansion.  Cast  iron  or  cast  steel  is  the  mate- 
rial used  for  their  construction,  while  the  joints  are  made  by  means 
of  flanges  fitted  with  rubber  gaskets. 

Table  5  gives  the  rate  of  flow  of  water  in  feet  per  miniHe 
through  pipes  of  various  sizes.  A  flow  of  10  gallons  per  minute 
for  each  100  H.  P.  of  boiler  equipment  should  be  allowed  without 
causing  an  excessive  velocity  of  flow  in  the  pipes. 

BOILER  FOUNDATIONS,  FURNACES  AND  DRAFT. 

The  economical  u.se  of  coal  depends,  to  a  large  extent,  on  the 
setting  of  the  boiler  and  proper  dimensions  of  the  furnaces. 
Internally-fired  boilers  require  support  only,  while  the  setting  of 
externally-fired  boilers  requires  provision  for  the  furnaces.  Com- 
mon brick,  together  with  fire  brick  for  the  lining  of  portions 
exposed  to  the  hot  gases,  are  used  almost  invariably  for  boiler 
settings.  It  is  customary  to  set  the  boiler  units  up  in  batteries 
of  two,  using  a  20-inch  wall  at  the  sides  and  a  12-inch  wall  be- 
tween the  two  boilers.  The  instructions  for  settings  furnished  by 


POWER   STATIONS  23 


the  manufacturers  should  be  carefully  followed  out  as  they  are 
based  on  conditions  which  give  the  best  results  in  the  operation  of 
their  boilers. 

Natural  Draft  is  the  most  commonly  used  and  is  the  most 
satisfactory  under  ordinary  circumstances.  In  determining  the 
size  of  the  chimney  necessary  to  furnish  this  draft,  the  following 
formula  is  given  by  Kent: 

.06  F  .06  Fv 

A—  — — — orA=   ( —      -)2 
V  h  A 

A  ==  area  of  chimney  in  sq.  ft. 
k  =  height  of  chimney  in  ft. 
F  =  pounds  of  coal  per  hour. 

The  height  of  chimney  should  be  assumed  and  the  area  calcu- 
lated, remembering  that  it  is  better  to  have  the  chimney  too  large 
than  too  small. 

The  chimney  may  be  of  either  brick  or  iron,  the  latter  having 
a  less  first  cost  but  requiring  repairs  at  frequent  intervals.  Gen- 
eral rules  for  the  design  of  a  chimney  may  be,  given  as  follows: 
The  external  diameter  of  the  base  should  not  be  less  than  ^  of 
the  height.  Foundations  must  be  of  the  best.  Interiors  should 
be  of  uniform  section  and  lined  with  fire  brick.  There  must  be  an 
air  space  between  the  lining  and  chimney  proper.  The  exterior 
should  have  a  taper  of  from  TX6  to  \-  i'nch  to  the  foot.  Flues 
should  be  arranged  symmetrically. 

Fig.  7  shows  the  construction  of  a  brick  chimney  of  good 
design,  this  chimney  being  used  with  boilers  furnishing  engines 
which  develop  14,000  H.  P. 

Mechanical  Draft  is  a  term  which  may  be  used  to  embrace 
both  forced  and  induced  draft.  The  different  systems  of  mechan- 
ical draft  are  described  in  books  on  boilers.  The  first  cost  of 
mechanical -draft  systems  is  less  than  that  of  a  chimney,  but 
the  operation  and  repair  are  much  more  expensive  and  there  is 
always  the  risk  of  break-down.  Artificial  draft  has  the  advan- 
tage that  it  can  be  varied  within  large  limits  and  it  can  be  increased 
to  any  desired  extent,  thus  allowing  the  use  of  low  grades  of  coal. 

Firing  of  Boilers  and  Handling  of  Fuel.  Coal  is  used  for 
fuel  to  a  greater  extent  than  any  other  material,  though  oil,  gas, 


POWER  STATIONS 


wood,  etc.,  are  used  in  some  localities.  Local  conditions,  such  as 
availability,  cost,  etc.,  should  determine  the  material  to  be  used 
and  no  general  rules  can  be  given.  Data  regarding  the  relative 

heating  values  of  different 
fuels  show  the  following 
general  iigures:  One  .pound 
of  petroleum,  about  \  of  a 
gallon,  is  equivalent,  when 
used  with  boilers,  to  1.8 
pounds  of  coal  and  there  is 
less  deterioration  of  the  fur- 
nace with  oil.  7it  to  12  cubic 
feet  of  natural  gas  are  re- 
quired as  the  equivalent  of 
one  pound  of  coal,  depending 
on  the  quality  of  the  gas.  2i 
pounds  of  dry  wood  is  as- 
sumed as  the  equivalent  of 
one  pound  of  coal. 

When  coal  is  used,  it 
requires  stoking  and  this 
may  be  accomplished  either 
by  hand  or  by  means  of  me- 
chanical stokers,  many  forms 
of  which  are  available.  Me- 
chanical stoking  has  the  ad- 
vantage over  hand  stoking 
that  the  fuel  may  be  fed  to 
the  furnace  more  uniformly 
and  the  fires  and  boilers  are 
not  subjected  to  sudden 
blasts  of  cold  air  as  is  the 
case  when  the  fire  doors  are 
opened  ;  a  poorer  grade  of 
coal  may  be  burned,  if  nec- 
essary, and  the  trouble  due 
to  smoke  is  much  reduced.  It  may  be  said  that  mechanical 
stokers  are  used  almost  universally  in  the  more  important  elec- 


Spo.ce 


Ground  Line 


Fig.  7. 


POWER  STATIONS  25 


trical  plants.  Economic  use  of  fuel  requires  great  care  in  firing, 
especially  if  it  is  done  by  hand. 

Where  gas  is  used,  the  tiring  may  be  made  nearly  automatic, 
and  the  same  is  true  of  oil  tiring,  though  the  latter  requires  more 
complicated  burners,  as  it  is  necessary  that  the  oil  be  vaporized. 

In  large  stations,  operated  continuously,  it  is  desirable  that, 
as  far  as  possible,  all  coal  and  ashes  be  handled  by  machinery, 
though'  the  difference  in  cost  of  operation  should  be  carefully  con- 
sidered before  installing  extensive  coal-handling  machinery.  Ma- 
chinery for  automatically  handling  the  coal  will  cost  from  $7.50  to 
$10  per  horse-power  rating  of  boilers  for  installation,  while  the  ash- 
handling  machinery  will  cost  from  $1.50  to  $3.00  per  horse  power. 

The  coal-handling  devices  usually  consist  of  chain -operated 
conveyors  which  hoist  the  coal  from  railway  cars,  barges,  etc.,  to 
overhead  bins  from  which  it  may  be  fed  to  the  stokers.  The 
ashes  may  be  handled  in  a  similar  manner,  by  means  of  scraper 
conveyors,  or  small  cars  may  be  used.  Either  steam  or  electricity 
may  be  used  for  driving  this  auxiliary  apparatus. 

It  is  always  desirable  that  there  be  generous  provision  for  the 
storage  of  fuel  sufficient  to  maintain  operations  of  the  plant  over 
a  temporary  failure  of  supply. 

STEAM  ENGINES  AND  TURBINES. 

The  choice  of  steam  prime  movers  is  one  which  is  governed 
by  a  number  of  conditions  which  can  be  treated  but  briefly  here. 
The  first  of  these  conditions  relates  to  the  speed  of  the  engine  to 
be  used.  There  is  considerable  difference  of  opinion  in  regard  to 
this  as  both  high  and  low-speed  plants  are  in  operation,  which  are 
giving  good  satisfaction.  Slow-speed  engines  have  a  higher  first 
cost  and  a  higher  economy.  Probably  in  sizes  up  to  250  K.W. 
the  generator  should  be  driven  by  high-speed  engines,  above  which 
the  selection  of  either  type  will  give  satisfaction  until  sizes  of  say 
above  500  indicated  horse  power,  when  the  slow-speed  type  is  to 
be  recommended.  Drop  valves  cannot  be  used  with  satisfaction 
for  speeds  above  about  100  revolutions  per  minute,  hence  high- 
speed engines  must  use  direct-driven  valve  gears,  usually  governed 
by  shaft  governors.  Corliss  valves  are  used  on  nearly  all  slow- 
•peed  engines. 


26  POWER  STATIONS 


The  steam  pressure  used  should  be  at  least  125  pounds  per 
square  inch  at  the  throttle  and  a  pressure  as  high  as  150  to  160 
pounds  is  to  be  preferred. 

Close  regulation   and  uniform  angular  velocity  are  required 

O  v 

for  driving  generators,  especially  alternators  which  are  to  operate 
in  parallel.  This  means  sensitive  and  active  governors,  carefully 
designed  fly-wheels  and  proper  -arrangement  of  cranks  when  more 
than  one  is  used. 

For  large  plants  or  plants  of  moderate  size,  compound  con- 
densing engines  are  almost  universally  installed.  The  advantage 
of  these  engines  in  increased  economy  are  in  part  counterbalanced 
by  higher  first  cost  and  increased  complications,  together  with  the 
pumps  and  added  water  supply  necessary  for  the  condensers. 
The  approximate  saving  in  amount  of  steam  is  shown  in  table  0, 
which  applies  to  a  500  horse-power  unit. 

TABLE  6. 

Pounds  or  Steam 
per  H.  P.  hour. 

Simpler  non-condensing 30 

Simple  condensing 22 

Compound  non-condensing 24 

Compound  condensing in 

Triple  expansion  engines  are  seldom  used  for  driving  electrical 
machinery  as  their  advantages  under  variable  loads  are  doubtful. 
Compound  engines  may  be  tandem  or  cross  compound  and  either 
horizontal  or  vertical.  The  use  of  cross-compound  engines  tends 
to  produce  uniform  angular  velocity,  but  the  cylinder  should  be  so 
proportioned  that  the  amount  of  work  done  by  each  is  nearly  equal. 
A  cylinder  ratio  of  about  3J  to  1  will  approximate  average  condi- 
tions. Either  vertical  or  horizontal  engines  may  be  installed,  each 
having  its  own  peculiar  advantages.  Vertical  engines  require  less 
floor  space,  while  horizontal  engines  have  a  better  arrangement  of 
parts.  Either  type  should  be  constructed  with  heavy  parts  and 
erected  on  solid  foundations. 

Recently  steam  turbines  have  come  into  use,  and  the  number 
of  stations  at  present  under  process  of  design  or  construction  which 
will  use  steam  turbines  is  very  large.  Several  types  of  turbines 
are  described  in  the  books  on  engines.  In  addition  to  these,  a 


POWER  STATIONS  27 


short  review  of  the  Curtis  turbine  will  not  be  out  of  place  since 
this  is  one  of  the  types  which  is. coming  into  extended  use. 

The  Curtis  turbine  is  divided  into  sections,  each  section  of 
which  may  contain  one,  two,  or  more,  revolving  sets  of  buckets 
and  stationary  vanes  supplied  with  steam  from  a  set  of  expansion 
nozzles.  By  this  arrangement  of  parts  the  work  is  divided  into 
stages,  the  nozzle  velocity  is  reduced  in  each  stage,  and  the  energy 
of  the  steam  is  effectively  given  up  to  the  rotating  parts.  This 
type  admits  of  lower  speeds  than  the  other  forms  of  turbines. 
Fig.  8.  shows  the  arrangement  of  nozzles,  buckets,  and  stationary 
blades  or  guiding  vanes  for  two  stages.  Governing  is  accom- 
plished by  shutting  off  "the  steam  from  some  of  the  nozzles.  A 
complete  Curtis  turbine  of  the  vertical  type,  direct  connected  to  a 
5,000  K.W.  three-phase  alternating-current  generator,  is  shown 
in  Fig.  9. 

The  advantages  claimed  for  this  turbine  are: 

1.  High  steam  economy  at  all  loads 

2.  High  steam  economy  with  rapidly  fluctuating  loads. 

'  3.  Small  floor  space  per  K.W.  capacity,  reducing  to  a  minimum 
the  cost  of  real  estate  and  buildings. 

4.  Uniform  angular  velocity. 

5.  Simplicity  iii  operation  and  low  expense  for  attendance. 

6.  Freedom  from  vibration. 

7.  Steam  economy  not  appreciably  impaired  by  wear  or  lack  of 
adjustment  in  long  service. 

8.  Adaptability  to  high  steam  pressure  and  high  superheat  without 
practical  difficulty  and  with  consequent  improvement  in  economy. 

9.  Condensed  water  is  kept  entirely  free  from  oil  and  can    be 
returned  to  the  boilers. 

Many  of  these  advantages  apply  equally  well  to  the  other 
types  of  turbines  now  on  the  market.  All  turbines  are  especially 
adapted  to  operation  with  superheated  steam. 

Engines  should  preferably  be  direct-connected  as  already 
stated,  but  this  is  not  always  feasible,  and  gearing,  belt,  or  rope 
drives  must  be  resorted  to.  Countershafts,  belt  or  rope  driven, 
arranged  with  pulleys  and  belts  for  the  different  generators,  and 
with  suitable  clutches,  are  largely  used  in  small  stations.  They 
consume  considerable  power  and  the  bearings  require  attention. 

Careful  attention  must  be  given  to  the  lubrication  of  all  run- 
ning  parts,  and  extensive  oil  systems  are  necessary  in  large  plants. 


28 


POWER  STATIONS 


In  sucli  systems  a  continuous  circulation  of  oil  over  the  bearings 
and  through  the  engine  cylinders  is  maintained  by  means  of  oil 
pumps.  After  passing  through  the  bearings,  the  machine  oil  goes 
to  a  properly  arranged  oil-filter  where  it  is  cleaned  and  then 
pumped  to  the  bearings  again.  A  similar  process  is  used  in  cyl- 


ill!      I      i 

DIAGRAM  OF  NOZZLES  AND  BUCKETS  IN  CURTIS  STEAM  TURBINE. 

Fig.   8. 

inder  lubrication,  the  oil  being  collected  from  the  exhaust  steam 
and  only  enough  new  oil  is  added  to  make  up  for  the  slight  amount 
lost.  The  latter  system  is  not  installed  as  frequently  as  the  con- 
tinuous system  for  bearings.  In  the  Curtis  turbine,  vertical  type, 
the  oil  is  forced  in  between  the  two  plates,  forming  the  step  bear- 
ing, at  such  a  pressure  that  a  thin  film  of  oil  is  constantly  main- 
tained between  these  plates.  It  may  be  arranged  so  that  if,  for 
any  reason,  this  pressure  fails,  the  steam  will  be  cut  off  from  the 


T&^A^^ 

OFTHt 

UNIVERSITY 


or 


POWER  STATIONS 


20 


turbine  automatically.  The  bearings  which  support  the  shafts 
used  with  the  generators  at  the  Niagara  Falls  Power  Companies' 
plants  are  generously  flooded  with  oil  and  the  turbines  are  arranged 
so  as  to  remove  a  great  deal  of  the  weight  of  the  rotating  part 
from  this  bearing. 

HYDRAULIC    PLANTS. 

Because  of  the  relative  ease  with  which  electrical  energy  may 
be  transmitted  long  distances,  it  has  become  quite  common  to  locate 


Fig.  9. 

large  power  stations  where  there  is  abundant  water  power,  and  to 
transmit  the  energy  thus  generated  to  localities  where  it  is  needed. 
This  type  of  plant  has  been  developed  to  the  greatest  extent  in  the 
western  part  of  the  United  States,  where  in  some  cases  the  trans- 
mission  lines  are  very  extensive.  The  power  houses  now  completed, 
or  in  the  course  of  erection  at  Niagara  Falls,  are  examples  of  the 
enormous  size  such  stations  may  assume. 


80 


POWER  STATIONS 


Water 


Before  deciding  to  utilize  water  power  for  driving  the  ma- 
chinery in  central  stations,  the  following  points  should  be  noted: 

1.  The  amount  of  water  power  available. 

2.  The  possible  demand  for  power. 

o.  Cost  of  developing  this  power  as  compared  with  cost  of  plants 
using  other  sources  of  power. 

4.  Cost  of  operation  compared  with  other  plants  and  extent  of 
transmission  lines. 

Hydraulic  plants  are  often  much  more  expensive  than  steam 

plants,  but  the  first  cost  is 
more  than  made  up  by  the 
saving  in  operating  ex- 
penses. 

Methods  for  the  devel- 
opment of  water  powers 
vary  with  the  nature  and 
amount  of  the  water  supply, 
and  they  may  be  studied 
best  by  considering  plants 
which  are  in  successful 
operation,  each  one  of 
which  has  been  a  special 
problem  in  itself.  A  full 
description  of  such  plants 

LOW  Water  would  be  too  extensive  to 

be  incorporated   here,  but 

Fig.  10.  they  can  be  found  in  the 

various  technical  journals. 

Water  Turbines  used  for  driving  generators  are  of  two  general 
classes,  reaction  turbines  and  impulse  turbines.  The  former  may  be 
subdivided  into  Parallel-flow,  Out  ward -flow,  and  Inward-flow  tur- 
bines. Parallel-flow  turbines  are  suited  for  low  falls,  not  exceeding 
30  feet.  Their  efficiency  is  from  70  to  72%.  Outward-flow  and 
inward-flow  turbines  give  an  efficiency  from  79  to  88%.  Impulse 
turbines  are  suitable  for  very  high  falls  and  should  be  used  from 
heads  exceeding  say  100  feet,  though  it  is  difficult  to  say  at  what 
head  the  reaction  turbine  would  give  place  to  the  impulse  wheel, 
as  reaction  turbines  are  giving  good  satisfaction  on  heads  in 
the  neighborhood  of  200  feet,  while  impulse  wheels  are  operated 


-I 


POWER  STATIONS 


31 


with  falls  of  but  80  feet.     The  Pelton  wheel  is  one  of  the  best 
known  types  of  impulse  wheels.    .An  efficiency  as  high  as  86%  is 


Fig.  11. 

claimed  for  this  type  of  wheel  under  favorable  conditions.     Fig. 
10  shows  a  reaction  wheel  and  Fig.  11  illustrates  a  Pelton  wheel. 

TABLE  7. 
Pressure  of  Water. 


Feet 
Head. 

Pressure 
Pounds  per 
Square  Inch. 

Feet 
Head. 

Pressure 
Pounds  per 
Square  Inch. 

Feet 
Head. 

Pressure 
Pounds  per 
Square  Inch. 

Feet 
Head. 

Pressure 
Pounds  per 
Square  Inch. 

10 

4.  .33 

105 

45.48 

200 

86.  63 

295 

127.78 

15 

6.49 

110 

47.64 

205 

88.80 

300 

129.95 

20 

8.66 

115 

49.81 

210 

90.96 

310 

134.28 

25 

10.82 

120 

51.98 

215 

93.13 

320 

138.62 

30 

12.99 

125 

54.15 

220 

95.30 

330 

142.95 

35 

15.16 

130 

56.31 

225 

97.46 

340 

147.28 

40 

17.32 

135 

58.48 

230 

99.  a3 

350 

151.61 

45 

19.49 

140 

60.64 

235 

101.79 

360 

155.94 

50 

21.65 

145 

62.81 

240 

103.90 

370 

160.27 

55 

23.82 

150 

64.97 

245 

106.13 

380 

164.61 

60 

25.99 

155 

67.14 

250 

108.29 

390 

168.94 

65 

28.15 

160 

69.31 

255 

110.46 

400 

173.27 

70 

30.32 

165 

71.47 

260 

112.62 

500 

216.58 

75 

32.48 

170 

73.64 

265 

114.79 

600 

259.90 

80 

34.65 

175 

75.80 

270 

116.96 

700 

303.22 

85 

36.82 

180 

77.97 

275 

119.12 

800 

346.54 

90 

38.98 

185 

80.14 

280 

121.29 

900 

389.86 

95 

41.15 

190 

82.30 

285 

123.45 

1000 

433.18 

100 

43.31 

195 

84.47 

290 

125.62 

The  fore  bay  leading  to  the  flume  should  be  made  of  such  size 
that  .the  velocity  of  water  does  not  exceed  1J  feet  per  second,  and 


POWER  STATIONS 


TABLE  8. 
Riveted  Hydraulic  Pipe. 


Diam.  of  Pipe 
in  inches. 

Area  of  Pipe 
in  sq.  inches. 

Thickness  of 
Iron  by  wire 
gauge. 

Head  in  Feet 
the  Pipe  will 
safely  stand. 

Cu.  ft.  Water 
Pipe  will  con- 
vey per  min. 
at  vel.  3  ft. 
per  sec. 

Weight  per 
lineal  ft.  in  Ibs. 

3 

7 

18 

400 

9 

2 

4 

12 

18 

350 

16 

2% 

4 

12 

16 

525 

16 

3 

5 

20 

18 

825 

25 

8V7 

5 

20 

16 

500 

25 

4% 

5 

20 

14 

675 

25 

5 

6 

28 

18 

296 

36 

4^ 

6 

28 

16 

487 

86 

6 

28 

14 

743 

.   36 

7% 

7 

38 

18 

254 

50 

^% 

7 

38 

16 

419 

50 

6% 

7 

38 

14 

640 

50 

8 

50 

16 

367 

63 

7% 

8 

50 

14 

560 

63 

9% 

8 

50 

12 

854 

63 

13 

9 

63 

16 

327 

80 

8%. 

9 
9 

63 

63 

14 
12 

499 
761 

80 
80 

10% 
14% 

10 

78 

16 

295 

100 

10 
10 
10 
10 

78 
78 
78 
78 

14 
12 
11 
10 

450 

687 
754 
900 

100 
100 
100 
100 

11% 
lo% 

17% 
19% 

11 

95 

16 

269 

120 

11 

95 

14 

412 

120 

13  4 

11 

95 

12 

626 

120 

ll¥ 

11 

95 

.  11 

687 

120 

11 

95 

10 

820 

120 

21  4 

12 

113 

16 

246 

142 

H% 

12 

113 

14 

377 

142 

14 

12 
12 

113 
113 

12 
11 

574 

630 

142 
142 

18% 
19% 

12 

113 

10 

753 

142 

22% 

13 

132 

16 

228 

170 

12 

13 

132 

14 

348 

170 

15 

13 

132 

12 

530 

170 

20 

13 

132 

11 

583 

170 

22 

13 

132 

10 

•  696 

170 

24% 

14 

153 

16 

211 

200 

13 

14 

153 

14 

324 

200 

16 

14 
14 

153 
153 

12 
11 

494 
543 

200 
200 

21% 

23% 

14 

153 

10 

648 

200 

26 

15 

176 

16 

197 

225 

13% 

15 

176 

14 

302 

225 

17 

15 

176 

12 

460 

225 

23 

15 

176 

11 

507 

225 

24% 

15 

176 

10 

606 

225 

28  2 

16 

201 

16 

185 

255 

14% 

16 

201 

14 

283 

255 

l?g 

16 

201 

12 

432 

255 

16 

201 

11 

474 

255 

26% 

POWER  STATIONS 


Riveted  Hydraulic  Pipe.     (Continued.) 


Diam.  of  Pipe 
in  inches. 

Area  of  Pipe 
in  sq.  inches. 

Thickness  of 
Iron  by  wire 
gange. 

Head  in  Feet 
the  Pipe  will 
safely  stand. 

Cu.  ft.  Water 
Pipe  will  con- 
vey per  niin. 
at  vel.  3  ft, 
per  sec. 

Weight  per 
lineal  ft,  in  Ibs 

16 

201 

10 

567 

255 

29% 

18 

254 

16 

165 

320 

18 

254 

14 

252 

320 

20% 

18 

254 

12 

385 

320 

18 

254 

11 

424 

820 

30  * 

18 

254 

10  - 

505 

320 

34 

20 

314 

16 

148 

400 

18 

20 

314 

14 

227 

400 

22% 

20 

314 

12 

346 

400 

30 

20 

314 

11 

380 

400 

82% 

20 

314 

10 

456 

400 

36% 

22 

380 

16 

135 

480 

20 

22 

380 

14 

206 

480 

24% 

22 

380 

12 

316 

480 

82% 

22 

380 

11 

347 

480 

35% 

22 

380 

10 

415 

480 

40 

24 

452 

14 

188 

570 

27% 

24 

452 

12 

290 

570 

85% 

24 

452 

11 

318 

570 

39 

24 

452 

10 

379 

570 

43% 

24 

452 

8 

466 

570 

53 

26 

26 

530 
530 

14 
12 

175 

267 

670 
670 

29% 
38% 

26 

530 

11 

294 

670 

42 

26 

530 

10 

352 

670 

37 

26 

530 

8 

432 

670 

57% 

28 

615 

14 

102 

775 

31% 

28 

615 

12 

247 

775 

41% 

28 

615 

11 

278 

775 

45 

28 

615 

10 

327 

775 

50% 

28 

615 

8 

400 

775 

61% 

30 

706 

12 

231 

890 

44 

30 

706 

11 

254 

890 

48 

30 

706 

10 

304 

890 

54 

30 

706 

8 

375 

890 

65 

30 

706 

7 

425 

890 

74 

36, 

1017 

11 

141 

1300 

58 

36 

1017 

10 

155 

1300 

67 

36 

1017 

8 

192 

1300 

78 

36 

1017 

7 

210 

1300 

88 

40 

1256 

10 

141 

1600 

71 

40 

1256 

8 

174 

1600 

86 

40 

1256 

7 

189 

1600 

97 

40 

1256 

6 

.213 

1600 

108 

•   40 

1256 

4 

250 

1600 

126 

42 

1385 

10 

135 

1760 

74% 

42 

1385 

8 

165 

1760 

91 

42 

1385 

7 

180 

1760 

102 

.  42 

1385 

6 

210 

1760 

114 

42  - 

1385 

4 

240 

1760 

133 

42 

1385 

i/ 

270 

1760 

137 

42 

1385 

3 

300 

1760 

145 

42 

1385 

5 

321 

1760 

177 

42    j    1385 

A 

363 

1760 

216 

34 


POWER  STATIONS 


it  should  be  free  from  abrupt  turns.  The  same  applies  to  the  tail 
race.  The  velocity  of  water  in  wooden  flumes  should  not  exceed 
7  to  8  feet  per  second.  Riveted  steel  pipe  is  used  for  the  penstocks 
and  for  carrying  water  from  considerable  distances  under  high 
heads.  In  some  locations  it  is  buried,  in  others  it  is  simply 
placed  on  the  ground.  Wooden -stave  pipe  is  used  to  a  large  extent 
when  the  heads  do  not  much  exceed  200  feet.  Table  7  gives  the 
pressure  of  water  at  different  heads,  while  Table  8  gives  considera- 
ble data  relating  to  riveted -steel  hydraulic  pipe. 

Governors  are  required  to  keep  the  speed  constant  under 
change  of  load  and  change  of  head.  Various  governors  are  manu- 
factured which  give  excellent  satisfaction. 

TABLE  9. 
Horse  Power  per  cubic  foot  of  water  per  minute  for  different  heads. 


Heads 
in 
Feet. 

Horse 
Power. 

Heads 
in 
Feet. 

Horse 
Power 

Heads 
in 
Feet. 

Horse 
Power. 

Heads 
in 
Feet. 

Horse 
Power. 

1 

.0016098 

170 

.273666 

330 

.531234 

-490 

.  788802 

20 

.032196 

180 

.289764 

340 

.547332 

500 

.804900 

80 

.048294 

190 

.305862 

350 

.563430 

520 

.837096 

40 

.064392 

200 

.321960 

360 

.579528 

540 

.869292 

50 

.080490 

210 

.338058 

370 

.595626 

560 

.901488 

GO 

.096588 

220 

.354156 

380 

.611724 

580 

.933684 

70 

.112686 

230 

.370254 

390 

.627822 

600 

.965880 

80 

.128784 

240 

.386352 

400 

.648920 

650 

1.046370 

90 

.144892 

250 

.402450 

410 

.660018 

700 

1.126860 

100 

.160980 

260 

.418548 

420 

.676116 

750 

1.207350 

110 

.177078 

270 

.434646 

430 

.692214 

800 

1.287840 

120 

.193176 

280 

.450744 

440 

.708312 

900 

1.448820 

130 

.209274 

290 

.466842 

450 

.724410 

1000 

1.609800 

140 

.225372 

300 

.  .482940 

460 

.740508 

1100 

1.770780 

150 

.241470 

310 

.499038 

470 

.756606 

160 

.257568 

320 

.515136 

480 

.772704 

GAS   ENGINES. 


There  are  at  present,  in  the  United  States,  several  successful 
electrical  installations  using  gas  engines  as  prime  movers,  while 


they  have  been  operated  abroad  for  a  greater  length  of  time, 
advantages  for  gas  engines  are  given  as  follows: 

1.  Minimum  fuel  and  heat  consumption. 

2.  Light-load  efficiency  is  higher  than  for  the  steam  engines. 

3.  Low  cost  of  operation  and  maintenance. 


The 


POWER  STATIONS 


4.     Simplification  of  equipment  and  small  number  of  auxiliaries. 


5.  No  heat  lost  due  to  radiation  when  engines  are  idle. 

0.  Quick  starting. 

7.  Extensions  may  be  easily  made. 

8.  High  pressures  are  limited  to  the  engine  cylinders. 

Fig.  12  shows  the  efficiency  and  amount  of  gas  consumed  by 
a  550  K.P.  engine,  Pittsburg  natural  gas  being  used. 

The  only  auxiliaries  needed  are  the  igniter  generators  and  the 

air  compressors,  with  a  pump  for  the  jacket  water  in  some  cases. 

These  may  be  driven  by  a  motor  or  by  a  separate  gas  engine. 

"The  jacket  water  may  be  utilized  for  heating  purposes  in  many 

plants.     Cooling  towers  may  be  installed  where  water  is  scarce. 


MENCY    TEST  OF  A  5?0  aH.R    FOUR   CYCLfc    GAS   ENGINE 
25"x30"  3  CYLINDER  VERTICAL  SINGLE-ACTING  VvPF  I 


Fig.  12. 

Parallel  operation  of  alternators  when  direct-driven  by  gas 
engines  has  been  successful,  a  spring  coupling  being  used  between 
the  engines  and  generators  in  some  cases  to  absorb  the  variation  in 
angular  velocity. 

The  fact  that  no  losses  occur,  due  to  heat  radiation  when  the 
machines  are  not  running,  and  the  lack  of  losses  in  piping,  add 
greatly  to  the  plant  efficiency.  If  producer  gas  or  blast  furnace 
gas  is  used,  a  larger  engine  must  be  installed,  to  give  the  same 
power,  than  when  natural  or  ordinary  coal  gas  is  used  Electric 


36  POWER  STATIONS 

stations  are  often  combined  with  gas  works,  and  gas  engines  can 
be  installed  in  such  stations  to  particular  advantage  in  many  cases. 

THE  ELECTRICAL  PLANT. 
GENERATORS. 

The  first  thing  to  be  considered  in  the  electrical  plant  is  the 
generators,  after  which  the  auxiliary  apparatus  in  the  way  of 
exciters,  controlling  switches,  safety  devices,  etc.,  will  be  taken  up. 
A  general  rule  which,  by  the  way,  applies  to  almost  all  machinery  for 
power  stations  is  to  select  apparatus  which  is  considered  as  "stand- 
ard" by  the  manufacturing  companies.  This  rule  should  be  fol- 
lowed for  two  reasons.  First,  reliable  companies  employ  men  who 
may  be  considered  as  experts  in  the  design  of  their  machines,  and 
their  best  designs  are  the  ones  which  are  standardized.  Second, 
standard  apparatus  is  from  15  to  25%  cheaper  than  serni-standard 
or  special  work,  owing  to  larger  production,  and  it  can  be  fur- 
nished on  much  shorter  notice.  Again,  repair  parts  are  more 
cheaply  and  readily  obtained. 

Specifications  should  call  for  performance,  and  details  should 
be  left,  to  a  very  large  extent,  to  the  manufacturers.  Following 
are  some  of  the  matters  which  may  be  incorporated  in  the  specifi- 
cations for  generators: 

1.  Type  and  general  characteristics. 

2.  Capacity  and  overload  with  heating  limits. 

3.  Commercial  efficiency  at  various  loads. 

4.  Excitation. 

5.  Speed  and  regulation. 

6.  Floor  space. 

7.  Mechanical  features. 

As  to  the  type  of  machine,  this  will  be  determined  by  the 
system  selected.  They  may  be  direct-current,  alternating-current^ 
single  or  polyphase,  or  as  in  some  plants  now  in  operation,  they 
may  be  double-current  generators.  The  voltage,  compounding, 
frequency,  etc.,  should  be  stated.  Direct-current  machines  are  sel- 
dom wound  for  a  voltage  above  600,  but  alternating-current  genera- 
tors maybe  purchased  which  will  give  as  high  as  15,000  volts  at  the 
terminals.  As  a  rule  it  is  well  not  to  use  an  extremely  high  volt- 
age for  the  generators  themselves,  but  to  use  step-up  transform- 
ers in  case  a  very  high  line  voltage  is  necessary.  Up  to  about 
75000  volts  generators  may  be  safely  used  directly  on  the  line. 


POWER  STATIONS  37 

Above  this  local  conditions  will  decide  whether  to  connect  the 
machine  directly  to  the  line  or  to  step  up  the  voltage.  Machines 
wound  for  high  potential  are  more  expensive  for  the  same  capacity 
and  efficiency,  but  the  cost  of  step-up  transformers  and  the  losses 
in  the  same  are  saved  by  using  such  machines,  so  that  there  is  a 
slight  gain  in  efficiency  which  may  be  utilized  in  better  regulation 
of  the  system,  or  in  lighter  construction  of  the  line.  On  the  other 
hand,  lightning  troubles  are  liable  to  be  aggravated  when  trans- 
formers are  not  used,  as  the  transformers  act  as  additional  protec- 
tion to  the  machines,  and  if  the  transformers  are  injured  they 
may  be  more  readily  repaired  or  replaced. 

The  following  voltages  are  considered  standard: 

Direct-current  generators  125,  250,  550-600. 

Alternating-current  systems,  high  pressure,  2,200,  6,000,  10,000, 
15,000,  20,000,  30,000,  40,000,  60,000. 

The  generators,  with  transformers  when  used,  should  be  capa- 
ble of  giving  a  no-load  voltage  10%  in  excess  of  these  figures. 
25  and  60  cycles  are  considered  as  standard  frequencies,  the 
former  being  more  desirable  for  railway  work  and  the  latter  for 
lighting  purposes. 

The  size  of  machines  to  be  chosen  has  been  briefly  considered. 
Alternators  are  rated  for  non-inductive  load  or  a  power  factor  of 
unity.  Aside  from  the  overload  capacity  to  be  counted  upon  as 
reserve,  the  Standardization  Report  of  the  American  Institute  of 
Electrical  Engineers  recommends  the  following  for  the  heating 
limits  and  overload  capacity  of  generators : 

Maximum  values  of  temperature  elevation, 

Field  and  armature,  by  resistance,  50°  C. 

Commutator  and  collector  rings  and  brushes,  by  thermometer,  55°  C. 

Bearings  and  other  parts  of  machine,  by  thermometer,  40°  C. 

Overload  capacity  should  be  25%  for  two  hours,  wTith  a  tem- 
perature rise  not  to  exceed  15°  above  full  load  values,  the  machine 
to  be  at  constant  temperature  reached  under  normal  load,  before 
the  overload  is  applied.  A  momentary  overload  of  50%  should  be 
permissible  without  excessive  sparking  or  injury.  Some  com- 
panies recommend  an  overload  capacity  of  50%  for  two  hours 
when  the  machines  are  to  be  used  for  railway  purposes. 


38  POWER  STATIONS 


As  a  rule,  generators  should  have  a  high  efficiency  over  a  con- 
siderable range  of  load,  although  the  nature  of  the  load  will  have 
much  to  do  with  this.  It  is  always  desirable  that  maximum  effi- 
ciency be  as  high  as  is  compatible  with  economic  investment. 

Table  10  gives  reasonable  efficiencies  which  may  be  expected 
for  generating  apparatus.  In  order  to  arrive  at  what  may  be  con- 
sidered the  best  maximum  efficiency  to  be  chosen,  the  cost  of  power 
generation  must  be  known,  or  estimated,  and  the  fixed  charges  on 
capital  invested  must  also  be  a  known  quantity.  From  the  cost 
of  power,  the  saving  on  each  per  cent  increase  in  efficiency  can  be 
determined,  and  this  should  be  compared  with  the  charges  on  the 
additional  investment  necessary  to  secure  this  increased  efficiency. 
A  certain  point  will  be  found  where  the  sum  of  the  two  will  be  a 
minimum. 

If  a  generator  is  to  be  run  for  a  considerable  time  at  light 
loads,  one  with  low  "  no-load  "  losses  should  be  chosen.  These 
losses  are  not  rigidly  fixed  but  they  vary  slightly  with  change 
of  load.  It  is  the  same  question  of  "  all-day  efficiency"  which 
is  treated,  in  the  case  of  transformers,  in  "  Power  Transmission  ". 
Under  no-load  losses  may  be  considered,  in  shunt-wound  gener- 
ators, friction  losses,  core  losses,  and  shunt-field  losses.  PR  losses 
in  the  series  field,  in  the  armature,  and  in  the  brushes,  vary  as  the 
square  of  the  load. 

Table  10. 
Average  Maximum  Efficiencies. 


K.W. 
5 

Per  Cent 
85 

10  

88 

25  

90 

50   

92 

150  . 

.  93 

200   94 

500  , 95 

1000 96 

Dynamos,  if  for  direct  current,  may  be  self-excited,  shunt-  or 
compound-wound,  or  separately  excited.  Separate  excitation  is  not 
recommended  for  these  machines.  Alternators  require  separate 
excitation,  though  they  may  be  compounded  by  using  a  portion  of 
the  armature  current  when  rectified  by  a  commutator.  Automatic 
regulation  of  voltage  is  always  desirable,  hence  the  general  use  of 


POWER  STATIONS  39 

compound-wound  machines  for  direct  currents.  Many  alternators 
using  rectified  currents  in  series  fields  for  keeping  the  voltage 
nearly  constant  are  in  service  in  small  plants  as  well  as  several  of 
the  so-called  "  compensated  "  alternators,  arranged  with  special 
devices  which  maintain  the  same  compounding  with  different 
power  factors.  The  latter  machine  gives  good  satisfaction  if 
properly  cared  for,  but  an  automatic  regulator,  governed  by  the 
generator  voltage  and  current,  which  acts  directly  on  the  exciter 
field,  is  taking  its  place.  The  capacity  of  the  exciters  must  be 
such  that  they  will  furnish  sufficient  excitation  to  maintain  normal 
voltage  at  the  terminals  of  the  generators  when  running  at  50% 
overload.  Table  11  gives  the  proper  capacity  of  exciter  for  the 
generator  listed. 

TABLE  ii. 

Exciters  for  Single=Phase  Alternating=Current  Generators. 

60  Cycles. 


Alternator 
Classification. 

Exciter 
Classification. 

y'         •         1J 

P-i        W         J/} 

'It  I 

8-    60-900 
8-    90-900 
8  -  120  -  900 
12  -  180  -  600 
16  -  300  -  450 

2 

2 
o 

2 

2 

-  1.5  -  1900 
-  1.5  -  1900 
-  1.5  -  1900 
-2.5-1900 
-4.5-1800 

If  direct-connected,  the  speeds  of  the  generators  will  be 
determined  by  the  prime  mover  selected.  If  belt-driven,  small 
machines  may  be  run  at  a  high  speed,  as  high-speed  machines  are 
cheaper  than  slow-  or  moderate -speed  generators.  In  large  sizes, 
this  saving  is  not  so  great. 

When  shunt- wound  dynamos  are  used,  the  inherent  regula- 
tion should  not  exceed  2  to  3%  for  large  machines.  For  alterna- 
tors, this  is  much  greater  and  depends  on  the  power  factor  of  the 
load.  A  fair  value  for  the  regulation  of  alternators  on  non- 
inductive  load  is  10  per  cent. 

Exciters  may  be  either  direct -connected  or  belted  to  the  shaft 
of  the  machine  which  they  excite,  or  they  may  be  separately 


40 


POWEK  STATIONS 


driven.  They  are  usually  compound-wound  and  furnish  current 
at  125  or  250  volts.  Separately  driven  exciters  are  preferred 
for  most  plants  as  they  furnish -a  more  flexible  system,  and  any 
drop  in  the  speed  of  the  generator  does  not  affect  the  exciter 
voltage.  Ample  reserve  capacity  of  exciters  should  be  installed, 
and  in  some  cases  storage  batteries,  used  in  conjunction  with 
exciters,  are  recommended  in  order  to  insure  reliability  of  service. 

Motor-generator  sets,  boosters,  frequency  changers,  and  other 
rotating  devices  come  under 
the  head  of  special  apparatus 
and  are  governed  by  the  same 
general  rules  as  generators. 

Transformers  for  step- 
ping the  voltage  from  that 
generated  by  the  machine  up 
to  the  desired  line  voltage,  or 
vice  versa,  at  the  substation, 
may  be  of  three  general  types, 
according  to  the  method  of 
cooling.  Large  transformers 
require  artificial  means  of 
cooling,  if  they  are  not  to  be 
too  bulky  and  expensive. 
They  may  be  air-cooled,  oil- 
cooled,  or  water-cooled. 

Air-cooled  transformers  are  usually  mounted  over  an  air- 
tight pit  fitted  with  one  or  more  motor-driven  blowers  which  feed 
into  the  pit.  The  transformer  coils  are  subdivided  so  that  no  part 
of  the  winding  is  at  a  great  distance  from  air  and  the  iron  is  pro- 
vided with  ducts.  Separate  dampers  control  the  amount  of  air 
which  passes  between  the  coils  or  through  the  iron.  Such  trans- 
formers give  good  satisfaction  for  voltages  up  to  20,000  or  higher, 
and  can  be  built  for  any  capacity.  Care  must  be  taken  to  see  that 
there  is  no  liability  of  the  air  supply  failing,  as  the  capacity  of  the 
transformers  is  greatly  reduced  when  not  supplied  with  air.  Fig. 
13  shows  a  three-phase  air-blast  transformer. 


POWER  STATIONS 


41 


Oil-cooled  transformers  have  their  cores  and  windings  placed 
in  a  large  tank  filled  with  oil.  The  oil  serves  to  conduct  the  heat 
to  the  case,  and  the  case  is  usually  either  made  of  corrugated  sheet 
metal  or  of  cast  iron  containing  deep  grooves,  so  as  to  increase  the 
radiating  surface.  These  transformers  do  not  require  such  heavy 


— c 


Fig.  14.    150  K.W.  Self-Cooled  Oil  Transformer. 

insulation  on  the  outside  of  the  coils  as  air-blast  machines  because 
the  oil  serves  this  purpose.  Simple  oil-cooled  transformers  are 
seldom  built  for  capacities  exceeding  250  K.W.  as  they  become 
too  bulky,  but  they  are  employed  for  the  highest  voltages  now  in 
use.  Fig.  14  shows  a  transformer  of  this  type. 


POWER  STATIONS 


^Water-cooled  transformers.  When  large  transformers  for  high 
voltages  are  required,  the  water-cooled  type  is  usually  selected. 
This  type  is  similar  to  an  oil-cooled  transformer,  but  with  water 


Fig.  15.     Water-Cooled  Transformer. 


tubes  arranged  in  coils  in  the  top.  Cold  water  passes  through 
these  tubes  and  aids  in  removing  heat  from  the  oil.  Some  types 
have  the  low- tension  windings  made  up  of  tubes  through  which 
the  water  circulates.  Water-cooled  transformers  must  not  have 


POWER  STATIONS 


43 


the  supply  of  cooling  water  shut  off  for  any  length  of  time  when 
under  normal  load  or  they  will  overheat.  Fig.  15  shows  a  water- 
cooled  transformer. 

For  connections  of  transformers,  see  "Power  Transmission". 


Fig.  15.    400  K. W.  Water  Cooled  Oil  Transformer. 

One  or  more  spare  transformers  should  always  be  on  hand  and 
they  should  be  arranged  so  that  they  can  be  put  into  service  on 
very  short  notice. 

Three-phase  transformers  allow  a  considerable  saving  in  floor 
space,  as  can  be  seen  by  referring  to  Fig.  16;  they  are  cheaper  than 
three  separate  transformers  which  make  up  the  same  capacity,  but 
they  are  not  as  flexible  as  a  single-phase  transformer  and  one 


44 


POWER  STATIONS 


complete  unit  must  be  held  for  a  reserve  or  "spare"  transformer. 
Storage  Batteries.     The  use  of  storage  batteries  for  central 
stations  and  substations  is  clearly  outlined  in  "  Storage  Batteries  ". 
The  chief  points  of  advantage  may  be  enumerated  as  follows: 


/^V^VAYAVAVAVAVAV 


Single-Phase  Air-Blast  Transformers.    Total  Capacity  3,000  K.W. 


L 


Three-Phase  Air-Blast  Transformers.    Total  Capacity  3,000  K.W. 
Fig.  16. 

1.  Reduction  in  fuel  consumption  due  to  the  generating  machinery 
being  run  at  its  greatest  economy. 

2.  Better  voltage  regulation. 

3.  Increased  reserve  capacity  and  less  liability  to  interruption  of 
service. 

The  main  disadvantage  is  the  high  cost. 

Switchboards.  The  switchboard  is  the  most  vital  part  of 
the  whole  system  of  supply,  and  should  receive  consideration  as 
such.  Its  objects  are:  to  collect  the  energy  as  supplied  by  the  gen- 
erators and  direct  it  to  the  desired  feeders,  either  overhead  or 


POWER  STATIONS  45 


under  ground;  furnish  a  support  for  the  various  measuring  instru- 
ments connected  in  service,  as  well  as  the  safety  devices  for  the 
protection  of  the  generating  apparatus;  and  control  the  pressure 
of  the  supply.  Some  of  the  essential  features  of  all  switch- 
boards are: 

1.  The  apparatus  aiid  supports  must  be  fire-proof. 

2.  The  couductiug  parts  must  iiot  overheat. 

3.  Parts  must  be  easily  accessible. 

4.  Live  parts  except  for  low  potentials  must  not  be  placed  011  the 
froiit  of  the  operating  panels. 

5.  The  arrangement  of  circuits  must  be  symmetrical  aiid  as  simple 
as  it  is  convenient  to  make  them. 

6.  Apparatus  must  be  arranged  so  that  it  is  impossible  to  make  a 
wrong  connection  that  would  lead  to  serious  results. 

7.  It  should  be  arranged  so  that  extensions  may  be  readily  made. 

There  are  two  general  types — in  the  first,  all  of  the  switching 
and  indicating  apparatus  is  mounted  directly  on  panels,  and  in  the 
second,  the  current-carrying  parts  are  at  some  distance  from  the 
panels,  the  switches  being  controlled  by  long  connecting  rods;  op- 
erated electrically  or  by  means  of  compressed  air.  The  first  may 
again  be  divided  into  direct-current  and  alternating-current  switch- 
boards. It  is  from  the  first  class  of  apparatus  that  the  switchboard 
gets  its  name  and  the  term  is  still  applied,  even  when  the  board 
proper  forms  the  smallest  part  of  the  equipment.  Switchboards 
have  been  standardized  to  the  extent  that  standard  generator,  ex- 
citer, feeder,  and  motor  panels  may  be  purchased  for  certain  classes 
of  work,  but  the  vast  majority  of  them  are  made  up  as  semi-stand- 
ard or  special. 

The  leads  which  carry  the  current  from  the  machines  to  the 
switches  should  be  put  in  with  very  careful  consideration.  Their 
size  should  be  such  that  they  will  not  heat  excessively  when  carry- 
ing the  rated  overload  of  the  machine,  and  they  should  preferably 
be  placed  in  fire-proof  ducts,  although  low-potential  leads  do  not 
always  require  this  construction.  Curves  showing  sizes  for  lead- 
covered  cables  for  different  currents  are  given  in  "  Power  Trans- 
mission ".  Table  12  gives  standard  sizes  of  wires  and  cables  to- 
gether with  the  thickness  of  insulation  necessary  for  different 
voltages.  Cables  should  be  kept  separate  as  far  as  possible  so 
that  if  a  fault  does  occur  on  one  cable,  neighboring  conductors 


46  POWER  STATIONS 

will  not  be  injured.  For  lamp  and  instrument  wiring,  such  as 
leads  to  potential  and  current  transformers,  the  following  sizes  of 
wire  are  recommended : 

No.  16  or  No.  14,  wiring  to  lamp  sockets. 

No.  12  wire,  &"  rubber  iiisulatioii,  all  other  small  wiring  under  <>00 
volts  potential. 

No.  12,  3V  rubber  insulation  for  primaries  of  potential  transformers 
from  600  to  3,500  volts. 

No.  8,  3y  rubber  insulation  for  primaries  of  potential  transformers 
up  to  6,600  volts. 

No.  8,  375  rubber  insulation  for  primaries  of  potential  transformers 
up  to  10,000  volts. 

No.  4,  |i  rubber  insulation  for  primaries  of  potential  transformers 
up  to  15,000  volts. 

No.  4,  jf  rubber  insulation  for  primaries  of  potential  transformers 
up  to  20,000  volts. 

No.  4,  45  rubber  insulation  for  primaries  of  potential  transformers 
up  to  25,000  volts. 

Where  high-tension  cables  leave  their  metallic  shields  they 
are  liable  to  puncture,  so  that  the  sheath  should  be  flared  out  at 
this  point  qnd  the  insulation  increased  by  the  addition  of  com- 
pound. Fig.  17  shows  such  cable  "bells,  as  they  are  called,  as 
recommended  by  the  General  Electric  Company. 

Central -station  switchboards  are  usually  constructed  of  panels 
about  90  inches  high,  from  16  inches  to  86  inches  wide,  and  1^ 
inches  to  2  inches  thick.  Such  panels  are  made  of  Blue  Vermont, 
Pink  Tennessee,  or  White  Italian  marble,  or  of  black  enameled 
slate.  Slate  is  not  recommended  for  voltages  exceeding  1,100.  The 
panels  are  in  two  parts,  the  sub-base  being  from  24  to  28  inches 
high.  They  are  polished  on  the  front  and  the  edges  are  beveled. 
Angle  and  tee  bars,  together  with  foot  irons  and  tie  rods,  form  the 
supports  for  such  panels,  and  on  these  panels  are  mounted  the  in- 
struments, main  switches,  or  controlling  apparatus  for  the  main 
switches,  as  the  case  may  be,  together  with  relays  and  hand  wheels 
for  rheostats  and  regulators.  Small  panels  are  sometimes  mounted 
on  pipe  supports. 

The  usual  arrangement  of  the  panels  is  to  have  a  separate 
panel  for  each  generator,  exciter,  and  feeder,  together  with  what  is 
known  as  a  station  or  total-output  panel.  In  order  to  facilitate 
extensions  and  simplify  connections,  the  feeder  panels  are  located 


POWER  STATIONS 


47 


at  one  end  of  the  board  and  the  generator  panels  are  placed  at  the 
other  end,  and  the  total-output  panel  between  the  two.  The  main 
bus  bars  extend  throughout  the  length  of  the  generator  and  feeder 
panels,  and  the  desired  connections  are  readily  made.  The  instru- 
ments required  are  very  numerous  and  a  brief  description  only  of 
a  few  of  the  more  important  can  be  given  here. 


TABLE  12. 
Standard  Wire  and  Cable. 

Wire  (Solid). 


Area. 

Diam. 
Inches. 

li 

Amps. 

Thickness  of  Rubber 
Insulation. 

Gauge. 

Circular 

Bare. 

h 

Con. 
Current 

1§    |       |        |         1         1        | 

B.  &  S 

Mils. 

' 

Capacity. 

>       «        '         _         S         1        « 

Special  Insulation. 

2,582 

.051 

No.  30  Dr. 

4 

16 

4,106j     .064 

30 

6 

3 

14 

6,530 

.081 

30 

10 

A 

A 

12 

16,510 

.128 

18 

25 

A 

A 

A 

3*2 

8 

26,2511     .162 

5 

40 

yV 

6 

41,743 

.204 

* 

60 

yV 

A 

A 

A 

u 

H 

u 

4 

66,373 

.257 

T5ff 

-    90 

A 

2 

83,695      .289 
105,593;      .325 

8  8 

110 
130 

¥ 

A 

A 

sV 

H 

1  4 
32 

H' 

1 
0 

133,079 
167,805 

.365 
.410 

a 

170 

205 

V 

t!4~ 

00 

000 

211,600 

.460 

ii 

250 

5 

til 

A 

A 

i<  ¥ 

li 

32 

H 

0000 

Cable. 

(Stranded.) 


Circular 
Mils. 

Diameter. 
Inches 
Bare. 

Terminal 
Drilling 

Con.  Curr. 
Capacity. 
Amps. 

Thickness  of  Rubber 
Insulation. 
(For  6000  V.  only.) 

250,000 

.568 

r 

290 

A 

300,000 

.637 

it" 

340 

A 

350,000 

.680 

\ 

380 

A 

400,000 

.735 

if 

420 

A 

500,000 

.820 

i!' 

500 

A 

600,000 

.900 

1'' 

575 

A 

800,000 

1.037 

H1 

710 

A 

1,000,000 

1.157 

4' 

830 

A 

1,500,000 

1.412 

H' 

1100 

i 

2.000,000 

1.65 

ir 

1350 

i 

POWER  STATIONS 


Wiped  joint 


alberene   soapstone 
x         or  wood 


-me—* 


H  9 


JZ3 


o.67compoun 

r 


iextra  insulation 


I  --------  Q  -----  yj  X  -3-150.  -f-2.  15  Y-t-4.3d 

Three-Conductor  Cable  Without  Joints. 


Wiped  joint 


alberene  soapstone 
-'•    or  wood  A-- 
C--+, 


t-  -  -5ssss-~ 

Jextra  insulation 

X  =3.150.  +2..  15  Y+4.3d 

Three-Conductor  Cable  With  Joints. 


Wiped  joint 


Two-Conductor  Cable  With  Joints. 


Wiped  joint 


alberene  soapstone 
3*^       or  wood     * 


no  67  compound 


rF* 

lextroi  insulation  •x.-s.o.+y- 

v 


Single-Conductor  Cable  With  Joints. 


VOLTS. 

A 

B 

C 

1) 

E 

F 

6600 

1 

12 

5 

% 

9V 

-/2 

1 

13200 

IX 

15 

8 

X 

4 

2 

26400 

2 

19 

14 

X 

7 

4 

i  -inch  Lead  or  jVinch  Brass  Bells.. 
Fig.  17. 


POWER  STATIONS 


Circuit 
Breaker 


For  direct  current  generator  panels  there  are  usually  re- 
quired: 

1  Main  switch 

1  Field  switch. 

1  Ammeter. 

1  Voltmeter. 

1  Field  rheostat  with  controlling  mechanism. 

1  Circuit  breaker 

Bus  bars  and  various  connections. 

These  may  be  arranged  in  any  suitable  order,  the  circuit 
breaker  being  preferably  located  at  the  top  so  that  any  arcing 
which  may  occur  will  not  injure  other  instruments.  Fig.  18  gives 
a  wiring  diagram  of  such  a  panel. 

The   main  switch  may  be  single  or  double  throw,  depending 

on  whether  one  or  two  sets  of  bus  •_ 

bars  are  used.  It  may  be  triple 
pole  as  shown  in  Fig.  18,  in 
which  the  middle  bar  serves  as 
the  equalizing  switch,  or  the  equal- 
izing switch  may  be  mounted  on  a 
pedestal  near  .the  machine,  in 
which  case  the  generator  switch 
would  be  double-pole. 

The  field  switch  for  large  ma- 
chines should  be  double-pole  fitted 
with  carbon  breaks  and  arranged 
with  a  discharge  resistance  con- 
sisting of  a  resistance  which  is 
thrown  across  the  terminals  of  the  field  just  before  the  main  cir- 
cuit is  opened.  One  voltmeter  located  on  a  swinging  bracket  at 
the  end  of  the  panel,  and  arranged  so  that  it  can  be  thrown  across 
any  machine  or  across  the  bus  bars  by  means  of  a  dial  switch,  is 
sometimes  used,  but  it  is  preferable  to  have  a  separate  meter  for 
each  generator. 

Small  rheostats  are  mounted  on  the  back  of  the  panel,  but 
large  ones  are  chain  operated  and  preferably  located  below  the 
floor,  the  controlling  hand  wheel  being  mounted-  on  the  panel. 

The  circuit  breaker  may  be  of  the  carbon  break  or  the  mag- 
netic blow-out  type.  Fig.  19  shows  circuit  breakers  of  both 


Ammeter 


Voltmeter 


D.P.  Field 


Discharqe 
Resistance 


Rheostat 


Generator 
Fig.  18. 


50 


POWER  STATIONS 


types.  Lighting  panels  for  low  potentials  are  often  fitted  with 
fuses  instead  of  circuit  breakers,  in  which  case  they  may  be  open 
fuses  on  the  back  of  the  panel  or  enclosed  fuses  on  either  the 
front  or  back  of  the  panel. 

Direct=Current   feeder  panels  contain: 

1  Ammeter. 

1  Circuit  Breaker. 

1  or  more  main  switches,  single-pole,  and  single-  or  double-throw. 

1  recording  wattmeter,  not  always  used 

Apparatus  for  controlling  regulators  when  such  are  used. 


Fig.  19. 

One  voltmeter  usually  serves  for  several  feeder  panels,  such  a 
meter  being  mounted  above  the  panels  or  on  a  swinging  bracket 
at  the  end.  Switches  should  preferably  be  of  the  quick-break 
type.  Fig.  20  shows  some  standard  railway  feeder  panels. 

Exciter  Panels  are  nothing  more  than  generator  panels  on  a 
small  scale. 


POWER    HOUSE    OF    NUW    YOrtK    SUBWAY. 

Showing  Five  of  the  Nine  12,000  Horse-Power  Allis-Chalmers  Engines. 


OF  THE 

UNIVERSITY 


POWER  STATIONS 


51 


Total  Output  Panels  contain  instruments  recording  the  total 
power  delivered  by  the  plant  to  the  switchboard.  Alternatiog- 
current  panels  for  potentials  up  to  1,100  volts  follow  the  same 
general  construction.  Synchronizing  devices  are  necessary  on  the 
generator  panels,  and  additional  ammeters  are  used  for  polyphase 
boards.  Sometimes  the  exciter  and  generator  panels  are  combined 


Fig.  19. 

in  one.  Fig.  21  shows  such  a  combination.  The  same  construction 
is  sometimes  used  for  voltages  up  to  2,500,  though  it  is  not  usually 
recommended.  The  paralleling  of  alternators  is  treated  in  "  Man- 
agement of  Dynamo  Electric  Machinery". 

For  the  higher  voltages,  the  measuring  instruments  are  no 
longer  connected  directly  in  the  circuit,  and  the  main  switch  is  not 
mounted  directly  on  the  panel.  Current  and  potential  trans- 


POWER  STATIONS 


formers  are  used  for  connecting  to  the  indicating  voltmeters  and 
ammeters,  and  the  recording  wattmeters  and  potential  transformers 
are  used  for  the  synchronizing  device.  These  transformers  are 
mounted  at  some  distance  from  the  panel,  while  the  switches  may 


RAILWAY  FEEDER  PANELS 


NO.  13559 


Engineering  Dept. 

General  Electric  Co. 


I  May  I9OO 


Fig.  20. 

be  located  near  the  panel  and  operated  by  a  system  of  levers,  or 
they  may  be  located  at  considerable  distance  and  operated  by  elec- 
tricity or  by  compressed  air. 

Oil  Switches  are  recommended  for  all  high  potential  work 
for  the  following  reasons:  By  their  use  it  is  possible  to  open  cir- 
cuits of  higher  potential  and  carrying  greater  currents  than  with 


POWER  STATIONS 


53 


any  other  type  of  switch.  They  may  be  made  quite  compact.  They 
may  readily  be  made  automatic  and  thus  serve  as  circuit  breakers 
for  the  protection  of  machines  and  circuits  when  overloaded. 


SWITCHBOARD  PANEL  FOR 

ONE  THREE-PHASE  ALTERNATING  CURRENT  GENERATOR 
TO  2500  VOLTS 


CL 

ASSIFICATK 

IN 

Type 

Volts 

Amperes 

Form 

Switch 

Field 
Ammeter 

synchronizing 
Device 

2500 

I3O 

.    with 

25OO 

I3O 

with 

withoot- 

2300 

130 

without 

with 

2500 

I3O 

without 

without 

23OO 

I3O 

with 

without 

2500 

130 

without 

Without    - 

Transformer  is  calibrated  with  Voltmeter  only.  Therefore  Synchronizing  Piuj  must  be  removes* 
•for  correct  Voltmeter  reodinj 

Fig.  21. 

There  are  several  types  on  the  market.  One  constructed  for 
three-phase  work,  to  be  cloned  by  hand  and  to  be  electrically 
tripped  or  opened  by  hand,  is  shown  in  Fig.  22.  This  shows  the 
switch  without  the  can  contain  ing  the  oil.  Fig.  23  shows  a  similar 
switch  hand-operated,  with  the  can  in  place.  Both  of  these 
switches  are  arranged  to  be  mounted  on  the  panel.  Fig.  24  shows 
how  the  same  switches  are  mounted  when  placed  at  some  distance 
from  the  panel.  For  high  voltages,  they  are  placed  in  brick  cells 
and  often  three  separate  single-pole  switches  are  used,  each  placed 
in  a  separate  cell  so  that  injury  to  the  contacts  in  one  leg  will  in 


POWER  STATIONS 


no  way  affect  the  other  parts  of  the  switch.  A  form  of  oil  switch 
used  for  the  very  highest  potentials  and  currents  met  with  in  prac- 
tice, is  shown  in  Fig.  25.  This  particular  switch  is  operated  by 
means  of  an  electric  motor,  though  it  may  be  as  readily  arranged  to 
operate  by  means  of  a  solenoid  or  by  compressed  air.  General 
practice  is  to  place  all  high-tension  bus  bars  and  circuits  in  separate 
compartments  formed  by  brick  or  cement,  and  duplicate  bus  bars 
are  quite  common. 


Fig.  22. 

Oil  switches  are  made  automatic  by  means  of  tripping  mag- 
nets,  which  are  connected  in  the  secondary  circuits  of  current 
transformers,  or  they  may  be  operated  by  means  of  relays  fed 
from  the  secondaries  of  current  transformers  in  the  main  leads. 
Such  relays  are  made  very  compact  and  can  be  mounted  on  the 


POWER  STATIONS 


55 


front  or  back  of  the  switchboard  panels.     The  wiring  of  such  trip- 
ping devices  is  shown  in  Fig.  26. 

With  remote  control  of  switches,  the  switchboard  becomes  in 
many  instances  more  properly  a  switch  house,  a  separate  building 
being  devoted  to  the  bus  bars,  switches,  and  connections.  In  other 
cases  a  framework  of  angle  bars  or  gas  pipe  is  made  for  the  support 
of  the  switches,  bus  bars,  current  and  potential  transformers,,  etc. 


Fig.  23. 


Additional  types  of  panels  which  may  be  mentioned  are  trans- 
former panels,  usually  containing  switching  apparatus  only;  rotary 
converter  panels  for  both  the  alternating  current  and  direct -current 
sides;  induction -motor  panels  and  arc- board  panels.  The  latter 


AAA 


Form  K  Oil  Switches  Located  Above  and  Form  K  Oil  Switches  Located  Below  and  Back 

Back  of  Operating  Panel.  of  Operat  ing  Panel. 


AA1 


-3 


Form  K  Oil  Switches  Located  Above  Form  K  Oil  Switches  Located  Back  of  Operating 

Operating  Panel.  Panel. 

Fig.  24, 


W     a 

B  I 


POWER  STA110NS 


57 


are  arranged  to  operate  with  plug  switches.  A  single  panel  used 
in  the  operation  of  series  transformers  on  arc-lighting  circuits  is 
shown  in  Fig.  27. 

Safety  Devices.  In  addition  to  the  ordinary  overload  trip- 
ping devices  which  have  already  been  considered,  there  are  various 
safety  devices  necessary  in  connection  with  the  operation  of  cen- 
tral stations.  One  of  the  most  important  of  these  is  the  liyhtning 
arrester.  For  direct-current  work,  the  lightning  arrester  takes  the 
form  of  a  single  gap  connected  in  series  with  a  high  resistance  and 
fitted  with  some  device  for  destroying  the  arc  formed  by  discharge 


Red  Indicatinq  Lamp 
/(Oil  Switch  Closed) 


losinq  Contact 


XDpeninq  Contact 
^reen  Indicatinq  La 
(Oil  Switch  Open) 


Automatic  Contact  Finqers 
Cam  Actuated 

Oil  Switch  in  Closed  Position 


Fig.  25. 

to  the  ground.  One  of  these  is  connected  between  either  side  of 
the  circuit  and  the  ground,  as  shown  diagrammatically  in  Fig.  28. 
A  "  kicking ?>  coil  is  connected  in  circuit  between  the  arresters  and 
the  machine  to  be  protected,  .to  aid  in  forcing  the  lightning  dis- 
charge across  the  gap.  In  railway  feeder  panels  such  kicking 
coils  are  mounted  on  the  backs  of  the  panels. 

For  alternating-current  work,  several  gaps  are  arranged  in 
series,  these  gaps  being  formed  between  cylinders  of  "  non-arcing" 
metal.  High  resistances  and  reactance  coils  are  used  with  these, 


58 


POWER  STATIONS 


Source 


Overload  Coil  R 


Source 


Load 


I  Current  . 
Transformer: 
tomatic: 
Oil  Switch 


Double  Pole  Relay 
.  Circuit  Normally  Closed 


Source 


O  pen  Ci  re  u  i  ti  ncj  Switch 


Trip  Coil 


Relay 


To  Continuous 
Current  Supply 

Fig.  20. 


as  in  direct-current  arresters. 
Fig.  29  shows  connections 
for  a  10,000-volt  lightning 
arrester.  Lighting  arresters 
should  always  be  provided 
with  knife  blade  switches  so 
that  they  can  be  discon- 
nected from  the  circuit  for 
inspection  and  repairs.  A 
typical  installation  of  light- 
ning arresters  is  shown  in 
Fig.  30. 

He  verse-current  relays  are 
installed  when  machines  or 
lines  are  operated  in  parallel. 
If  two  or  more  alternators 
are  running  and  connected 
to  the  same  set  of  bus  bars, 
and  one  of  these  should  fail 
to  generate  voltage  by  the 
opening  of  the  field  circuit, 
or  some  other  cause,  the 
other  machine  would  feed 
into  this  generator  and 
might  cause  considerable 
damage  before  the  current 
flowing  would  be  sufficient 
to  operate  the  circuit  breaker 
by  means  of  the  overload  trip 
coils.  To  avoid  this,  re- 
verse-current relays  are  used. 
They  are  so  arranged  as  to 
operate  at  say  J  the  normal 
current  of  the  machine  or 


line,  but  to  operate  only  wThen  the  power  is  being  delivered  in  the 
wrong  direction. 

Speed  limit  devices  are  used  on  both  engines  and  rotary  con- 
verters  to  prevent  racing  in  the  one  case  and  running  away  in  the 


POWER  STATIONS 


59 


second.  Such  devices  act  on  the  steam  supply  of  engines  and  on 
the  direct-current  circuit  breakers  of  rotary  converters,  respectively. 

Complete  wiring  diagram  for  a  railway  switchboard  is  shown 
in  Fig.  81. 

Substations.  Substations  are  for  the  purpose  of  transform- 
ing the  high  potentials  down  to  such  potentials  as  can  be  used  on 


motors  or  lamps,  and  in  many  cases  to  convert  alternating  current 
into  direct  current.  Step-down  transformers  do  not  differ  in  any 
respect  from  step-up  transformers.  Either  motor-generator  sets 
or  rotary  converters  may  be  used  to  change  from  alternating  to 
direct  current.  The  former  consist  of  synchronous  or  induction 
motors,  direct  connected  to  direct-current  generators,  mounted  on 


60 


POWER  STATIONS 


the  same  bedplate.  The  generator  may  be  shunt  or  compound 
.wound,  as  desiretl.  Rotary  converters  are  direct-current  genera- 
tors, though  specially  designed;  they  are  fitted  with  collector  rings 
attached  to  the  winding  at  definite  points.  The  alternating  cur- 
rent is  fed  into  these  rings  and  the  machine  runs  as  a  synchronous 

Connections  for  series  arc  liahtincj  circuits  up  to  eooo  volts 
qenerator       ,reacta.nce  coil 


cjround 


Connections  forliqhtinq  or  power  circuits 
uptoQ50  volts  (metallic  circuits)  J 

qenercttor       ^   reactance  coil 


motor 


Connections  for  railway  circuits  up  to  eso  volts 
reactance  coil          (one  side  a  rounded) 

qenercL- 

~    tor 


li 

Reaction  coil  is 
composed  ofes  of 
conductor  wound 
in  acoil  of  two  or 
more  turns  as  con 
venient- 

1 

I 

99 

1 

i 

1 

Fig.  28. 

motor,  while  direct  current  is  delivered  at  the  commutator  end. 
There  is  a  fixed  relation  between  the  voltage  applied  to  the  alter- 
nating-current side  and  the  direct-current  voltage,  which  depends 
on  the  shape  of  the  wave  form,  losses  in  the  armature,  pole  pitch 
of  the  machine,  method  of  connection,  etc.  The  generally  accepted 
values  are  as  follows: 


MANHATTAN    74th    ST.     POWER    STATION,     NEW    YORK. 

Showing  Carey's  Carbonate  of  Magnesia  Pipe  Coverings.    Steam  Connections. 


POWER  STATIONS 


TABLE  13. 

Full  Load  Ratios. 

Current.  Potential. 

Continuous : 100 

Two-phase         (  550  volts .  72.5 


and  Six-phase 
(diametrical) 
Three-phase 
and  Six-phase 
(  Y  or  delta) 


•{  250 
(125 
(  550 
1  250 
(  125 


73 

78.5 

62 

62 

63 


IOOOOV 


The   increase  of   capacity  of   six-phase   machines    over  other 
machines  of  the  same  size  is  given  in  Table  14. 

This  increase  is  due  to 

the  fact  that,  with  a  greater  Alternator^^Reactance  Coil 
number  of  phases,  less  of  the 
winding  is  traversed  by  the 
current  which  passes  through 
the  converter.  The  saving 
by  increasing  the  number  of 
phases  beyond  six  is  but 
slight  and  the  system  be- 
comes too  complex.  Ilotary 
converters  may  be  over-com- 
pounded by  the  addition  of 
series  fields,  provided  the  re- 
actance in  the  alternating  cir- 
cuits be  of  a  proper  value. 
It  is  customary  to  insert  re- 
actance coils  in  the  leads  from 
the  low-tension  side  of  the 
step-down  transformers  to 
the  collector  rings  to  bring 

the  reactance  to  a  value  which  will  insure  the  desired  compounding. 
Again,  the  voltage  may  be  controlled  by  means  of  induction  regu- 

TABLE  14. 
Capacity  Ratios. 

Continuous-current  generator 100 

Single-phase  converter 85 

Two-phase  converter 164 

Three-phase  converter 184 

Six^phase  converter 196 


POWER  STATIONS 


POWER  STATIONS  63 


lators  placed  in  the  alternating-current  leads.  Motor-generatoiM 
are  more  costly  and  occupy  more  space  than  rotary  converters,  but 
the  regulation  of  the  voltage  is  much  better  and  they  are  to  be 
preferred  for  lighting  purposes. 

Buildings.  The  power  station  usually  has  a  building  devoted 
entirely  to  this  work,  while  the  substations,  if  small,  are  often 
made  a  part  of  other  buildings.  While  the  detail  of  design  and 
construction  of  the  buildings  for  power  plants  belongs  primarily 
to  the  architect,  it  is  the  duty  of  the  electrical  engineer  to  arrange 
the  machinery  to  the  best  advantage,  and  he  should  always  be  con- 
sulted in  regard  to  the  general  plans  at  least,  as  this  may  save 
much  time  and  expense  in  the  way  of  necessary  modifications. 
The  general  arrangement  of  the  machinery  will  be  taken  up  later, 
but  a  few  points  in  connection  with  the  construction  of  the  build- 
ings and  foundations  will  be  considered  here. 

Space  must  be  provided  for  the  boiler, — this  may  be  a  sepa- 
rate building  —  engine  and  dynamo  room,  general  and  private 
offices,  store  rooms  and  repair  shops.  Very  careful  consideration 
should  be  given  to  each  of  these  departments.  The  boiler  room 
should  be  parallel  with  the  engine  room,  so  as  to  reduce  the  neces- 
sary amount  of  steam  piping  to  a  minimum,  and  if  both  rooms 
are  in  the  same  building  a  brick  wall  should  separate  the  two,  no 
openings  which  would  allow  dirt  to  come  from  the  boiler  room  to 
the  engine  room  being  allowed.  The  height  of  both  boiler  and 
engine  rooms  should  be  such  as  to  allow  ample  headway  for  lifting 
machinery  and  space  for  placing  and  repairing  boilers,  while  pro- 
vision should  be  made  for  extending  these  rooms  in  at  least  one 
direction.  Both  engine  and  boiler  rooms  should  be  fitted  with 
proper  traveling  cranes  to  facilitate  the  handling  of  the  units.  In 
some  cases  the  engines-  and  dynamos  occupy  separate  rooms,  but 
this  is  not  general  practice.  Ample  light  is  necessary,  especially 
in  the  engine  rooms.  The  size  of  the  offices,  store  rooms,  etc.,  will 
depend  entirely  on  local  conditions. 

The  foundations  for  both  the  walls  and  the  machinery  must 
be  of  the  very  best.  It  is  well  to  excavate  the  entire  space  under 
the  engine  room  to  a  depth  of  eight  to  ten  feet  so  as  to  form 
a  basement,  while  in  most  cases  the  excavations  must  be  made  to  a 
greater  depth  for  the  walls.  Foundation  trenches  are  sometimes 


D.P.S.T.D.R.SW.    D.P.S.T.Diseh.  Res 
RH'.  Exciter  Rheostat. 


POWER  STATIONS 


65 


filled  with  concrete  to  a  depth  sufficient  to  form  a  good  under- 
footing.  The  area  of  the  foundation  footing  should  be  great  enough 
to  keep  the  pressure  within  a  safe  limit  for  the  quality  of  the  soil. 


The  walls  themselves  may  be  of  wood,  brick,  stone,  or  concrete. 
Wood  is  used  for  very  small  stations  only,  while  brick  may  be 
used  alone  or  in  conjunction  with  steel'f raining,  the  latter  con- 
struction being  used  to  a  considerable  extent.  If  brick  alone  is 


POWER  STATIONS 


used,  the  walls  should  never  be  less  than  twelve  inches  thick,  and 
eighteen  to  twenty  inches  is  better  for  large  buildings.  They 
must  be  amply  reinforced  with  pilasters.  Stone  is  used  only  for 
the  most  expensive  stations.  The  interior  of  the  wralls  is  formed 
of  glazed  brick,  when  the  expense  of  such  construction  is  war- 
ranted. In  iireproof  construction,  which  is  always  desirable  for 
power  stations,  the  roofs  are  supported  by  steel  trusses  and  take  a 
great  variety  of  forms.  Fig.  32  shows  what  has  been  recommended 
as  standard  construction  for  lighting  stations,  showing  both  brick 
and  wood  construction.  The  floors  of  the  engine  room  should  be 


made  of  some  material  which  will  not  form  grit  or  dust.  Hard 
tile,  nnglazed,  set  in  cement  or  wood  floors,  is  desirable.  Storage 
battery  rooms  should  be  separate  from  all  others  and  should  have 
their  interior  lined  with  some  material  which  will  not  be  affected 
by  the  acid  fumes.  The  best  of  ventilation  is  desirable  for  all  parts 
of  the  station,  but  is  of  particular  importance  in  the  dynamo  room 
if  the  machines  are  being  heavily  loaded.  Substation  construction 
does  not  differ  from  that  of  central  stations  when  a  separate  build- 
ing is  erected.  They  should  be  fireproof  if  possible. 

The  foundations  for  machinery  should  be  entirely  separate 
from  those  of  the  building.  Not  only  must  the  foundations  be 
stable,  but  in  some  locations  it  is  particularly  desirable  that  no 


POWER  STATIONS 


67 


vibrations  be  transmitted  to  adjoining  rooms  and  buildings.  A 
loose  or  sandy  soil  does  not  transmit  such  vibrations  readily,  but 
drm  earth  or  rock  transmits  them  almost  perfectly.  Sand,  wool, 
tiair,  felt,  mineral  wool,  and  asphaltum  concrete  are  some  of  the 
materials  used  to  prevent  this.  The  excavation  for  the  foundation  is 
made  from  two  to  three  feet  deeper  and  two  to  three  feet  wider  on 
all  sides  than  the  foundation,  and  the  sand,  or  whatever  material 
is  used,  occupies  this  extra  space. 


for  bncK  foundation  a  1 2"  footing  of 
concrete  should  be  laid.  Depth  orfoondL- 
ation  must,  be  aoverr»eo'  toy  t-he  char- 
acter  of  the  soil  Batter  Ito6. 

Foundation  timbers  and  flooring  snould. 
be  independent  of  station  floor. 


Fig.  34. 

Brick,  stone,  or  concrete  is  used  for  building  up  the  greater 
part  of  machinery  foundations,  the  machines  being  held  in  place 
by  means  of  bolts  fastened  in  masonry.  A  template,  giving  the 
location  of  all  bolts  to  be  used  in  holding  the  machine  in  place, 
should  be  furnished,  and  the  bolts  may  be  run  inside  of  iron  pipes 
with  an  internal  diameter  a  little  greater  than  the  diameter  of  the 
bolt.  This  allows  some  play  to  the  bolt  and  is  convenient  for  the 
final  alignment  of  the  machine.  Fig.  33  gives  an  idea  of  this  con- 
struction. The  brickwork  should  consist  of  hard-burned  brick  of 
the  best  quality,  and  should  be  laid  in  cement  mortar.  It  is  well 
to  fit  brick  or  concrete  foundations  with  a  stone  cap,  forming  a 
level  surface  on  which  to  set  the  machinery,  though  this  is  not 
necessary.  Generators  are  sometimes  mounted  on  wood  bases  to 


68 


POWER  STATIONS 


furnish  insulation  for  the  frame.  Fig.  34  shows  the  foundation 
for  a  150  K.W.  generator,  while  Fig.  85  shows  the  foundation  for 
a  rotary  converter. 


For  brick  foundation  a  I2"footing  of  concrete  should 
be  lai.d  Depth  of  foundation  must,  be  governed  by  the 
character  of  the  soil-  Batter  I  to  6- 

Fig.  35. 

Station  Arrangement.  A  few  points  have  already  been 
noted  in  regard  to  station  arrangement,  but  the  importance  of  the 
subject  demands  a  little  further  consideration.  Station  arrange- 
ment depends  chiefly  upon  two 
facts — the  location  and  the  ma- 
chinery to  be  installed.  Un- 
doubtedly the  best  arrangement 
is  with  all  of  the  machinery  on 
one  floor  with,  perhaps,  the  oper- 
ating switchboard  mounted  on  a 
gallery  so  that  the  attendants 
may  have  a  clear  view  of  all  the 
machines.  Fig.  36  shows  the 
simplest  arrangement  of  a  plant 
using  belted  machines.  Fig.  37 
shows  an-  arrangement  of  units 
where  a  jack  shaft  is  used.  Direct -current  machines  should  be 
placed  so  that  the  brushes  and  commutators  are  easily  accessible 
and  the  switchboard  should  be  placed  so  as  to  not  be  liable  to 
accidents,  such  as  the  breaking  of  a  belt  or  a  fly-wheel. 


£/VG/A/£'S  DYNAMOS 

SWtTCH    BOAFU3 


CNG/NE.    ROOM 


Fig.  36. 


POWER  STATIONS 


69 


BOtLEF*  HOUSE 


ENGtNE  ROOM 


Fig.  37. 


When  the  cost  of  real  estate  prohibits  the  placing  of  all  of 
the  machinery  on  one  floor,  the  arrangements  shown  in  Fig.  38 
may  be  used  when  the  machines  are  belted.  It  is  always  desirable 
to  have  the  engines  oh  the  main  floor,  as  they  cause  considerable 
vibration  when  not  mounted 
on  the  best  of  foundations. 
The  boilers,  while  heavy,  do 
not  cause  such  vibration  and 
they  may  be  placed  on  the 
second  or  third  floor.  Belts 
should  not  be  run  vertically, 
as  they  must  be  stretched  too 
tightly  to  prevent  slipping. 

Fig.  39  shows  a  large 
station  using  direct-connected 
units,  while  Fig.  40  shows  the  arrangement  of  the  turbine  plant 
of  the  Boston  Edison  Electric  Illuminating  Company.  This  sta- 
tion will  contain  twelve  such  5,000  K.W.  units  when  completed. 
Note  the  arrangement  of  boilers  when  several  units  are  required 
for  a  single  prime  mover.  The  use  of  a  separate  room  or  building 

for  the  cables,  switches,  and 
operating  boards  is  becoming 
quite  common  for  high-tension 
generating  plants.  The  remark- 
able saving  in  floor  space  brought 
about  by  the  turbine  is  readily 
seen  from  Fig.  41.  The  total 
floor  space  occupied  by  the  new 
Boston  station  is  2.64  square 
feet  per  K0W.  This  includes 
boilers — of  which  there  are  eight, 
each  512  H.P.  for  each  unit- 
turbines,  generators,  switches, 
and  all  auxiliary  apparatus. 

When  transformers  are  used 
for  raising  the  voltage,  they  may 

be  placed  in  a  separate  building,  as  is  the  case  at  Niagara  Falls,  or 
the  transformers  may  be  located  in  some  part  of  the  dynamo  room, 
preferably  in  a  line  parallel  to  the  generators. 


BOfL  £H  HOUSE. 


ENGfNE    ROOM 


Fig.  39. 


70 


POWER  STATIONS 


Fig.  42  shows  the  arrangement  of  units  in  an  hydraulic  plant. 
Fig.  43  is  a  good  example  of  the  practice  in  substation  arrange- 
ment. Here  the  switchboard  is  mounted  at  one  end  of  the  room, 
while  the  rotary  converters  and  transformers  are  arranged  along 


either  side  of  the  building. 


L/NE 


ENG//VE 


GROUND 


"N 


ENG/NE 


Fig.  38. 


Large  cable  vaults  are 
installed  at  the  stations 
operating  on  underground 
systems,  the  separate  ducts 
being  spread  out,  and 
sheet-iron  partitions  erect- 
ed to  prevent  damage  be- 
ing- done  to  cables  which 

t~) 

were  not  originally  de- 
fective, by  a  short  circuit 
in  any  one  feeder. 

Station  Records.    In 

order  to  accurately  deter- 
mine the  cost  of  gener- 
ating power  and  to  check 
up  on  uneconomical  or 
improper  methods  of  oper- 
ation and  lead  to  their  im- 
provement,  accurately 
kept  station  records  are  of 
the  utmost  importance. 
Such  records  should  con- 
sist of  switchboard  rec- 
ords, engine-room  records, 
boiler-room  records,  and 
distributing-system  rec- 
ords. Such  records  accu- 


rately kept  and  properly  plotted  in  the  form  of  curves,  serve  admir- 
ably for  the  comparison  of  station  operations  from  day  to  day  and 
for  the  same  periods  for  different  years.  It  pays  to  keep  thesn 
records  even  when  additional  clerical  force  must  be  employed. 

Switchboard  records  consist,  in  alternating  stations,  of  daily 
readings  of  feeder,  recording  wattmeters,  and  total  recording  watt- 


POWER  STATIONS 


71 


meter,  together  with  voltmeter  and  ammeter  readings  at  intervals 
of  about  15  minutes  in  some  cases  to  check  upon  the  average 
power  factor  and  determine  the  general  form  of  the  load  curve. 
For  direct-current  lighting  systems  volt  and  ampere  readings  serve 
to  give  the  true  output  of  the  sta- 
tions, and  curves  are  readily  plotted 
from  these  readings.  The  voltage 
should  be  recorded  for  the  bus  bars 
as  well  as  for  the  centers  of  distri- 
bution. 


Indicator  diagrams  should  be  taken  from  the  engines  at  fre- 
quent intervals  for  the  purpose  of  determining  the  operation  of 
the  valves.  Engine-room  records  include  labor,  use  of  waste  oil 
and  supplies,  as  well  as  all  repairs  made  on  engines,  dynamos  and 
auxiliaries. 


be 


POWER  STATIONS 


Boiler-room  records  include  labor  and  repairs,  amount  of 
coal  used,  which  amount  may  be  kept  in  detail  if  desirable,  amount 
of  water  used,  together  with  steam-gauge  record  and  periodical 
analysis  of  flue  gases  as  a  check  on  the  methods  of  firing. 

Records  for  the  distributing  system  include  labor  and  ma- 
terial used  for  the  lines  and  substations.  For  multiple- wTire 


POWER  STATIONS  75 


systems,  frequent  readings  of  the  current   in  the  different  feeders 
will  serve  as  a  check  on  the  balance  of  the  load. 

The  cost  of  generating  power  varies  greatly  with  the  rate  at 
which  it  is  produced  as  well  as  upon  local  conditions.  Station 
operating  expenses  include  cost  of  fuel,  water,  waste,  oil,  etc.,  cost 
of  repairs,  labor,  and  superintendence.  Fixed  charges  include, 
insurance,  taxes,  interest  on  investment,  depreciation,  and  general 
office  expenses.  Total  expenses  divided  by  total  kilowatt  hours 
gives  the  cost  of  generation  of  a  kilowatt  hour.  The  cost  of  dis- 
tributing a  kilowatt  hour  may  be  determined  in  a  similar  manner. 
The  rate  of  depreciation  of  apparatus  differs  greatly  with  different 
machines,  but  the  following  figures  may  be  taken  as  average  values, 
these  figures  representing  percentage  of  first  cost  to  be  charged  up 
each  year  : 

Fireproof  buildings  from  2  to  3  per  cent. 

Frame  buildings  from  5  tc  8  per  cent. 

Dynamos  from  2  to  4  per  cent. 

Prime  movers  from  2%  to  5  per  cent. 

Boilers  from  4  to  5  per  cent 

Overhead  lines,  best  constructed,  o  to  10  per  cent. 

More  poorly  constructed  lines  20  to  HO  per  cent 

Badly  constructed  lines  40  to  (50  per  cent 

Underground  conduits  2  per  cent. 

Lead  covered  cables  2  per  cent. 

flethods  of  Charging  for  Power.  There  are  four  methods 
used  for  charging  consumers  for  electrical  energy,  namely,  the  fiat- 
rate  or  contract  system,  the  meter  system,  the  two-rate  meter  sys- 
tem, and  a  system  by  which  each  customer  pays  a  fixed  amount 
depending  on  the  maximum  demand  and  in  addition  pays  at  a 
reasonable  rate  for  the  power  actually  used.  In  the  flat-rate 
system,  each  customer  pays  a  certain  amount  a  year  for  service, 
this  amount  being  based  on  the  estimated  amount  of  power  to  be 
used.  These  rates  vary,  depending  on  the  hours  of  the  day  during 
which  the  power  is  to  be  used,  being  greatest  if  the  energy  is  to 
be  used  during  peak  hours.  It  is  an  unsatisfactory  method  for 
lighting  service,  as  many  customers  are  liable  to  take  advantage 
of  the  company,  burning  more  lights  than  contracted  for  and  at 
different  hours,  while  the  honest  customer  must  pay  a  higher  rate 
than  is  reasonable  in  order  to  make  the  station  operation  profitable. 


76 


POWER  STATIONS 


This  method  serves  much  better  when  the  power  is  used  for  driving 
motors,  and  is  used  largely  for  this  class  of  service. 

The  simple  meter  method  of  charging  serves  the  purpose 
better  for  lighting,  but  the  rate  here  is  the  same  no  matter  what 
hour  of  the  day  the  currenHs  used.  Obviously,  since  machinery 


Fig.  43. 

is  installed  to  carry  the  peak  of  the  load,  any  power  used  at  this 
time  tends  to  increase  the  capital  outlay  from  the  plant,  and  users 
should  be  required  to  pay  more  for  the  power  at  such  times. 

The  two-meter  rate  accomplishes  this  purpose  to  a  certain 
extent.  The  meters  are  arranged  so  that  they  record  at  two  rates, 
the  higher  rate  being  used  during  the  hours  of  heavy  load. 

There  are  several  methods  of  carrying  out  the  fourth  scheme. 
In  the  Brighton  System,  a  fixed  charge  is  made  each  month, 
depending  on  the  maximum  demand  for  power  during  the  previous 
month,  a  regular  schedule  of  such  charges  being  made  out,  based 
on  the  cost  of  the  plant.  An  integrating  wattmeter  is  used  to 
record  the  energy  consumed,  while  a  so-called  "  demand  meter  " 
records  the  maximum  rate  of  demand. 


POWER  TRANSMISSION, 

ELECTRICAL. 


The  subject  of  power  transmission  is  a  very  broad  one ;  deal- 
ing with  the  transmission  and  distribution  of  electrical  energy,  as 
generated  by  the  dynamo  or  alternating-current  generator,  to  the 
receivers.  The  receivers  may  be  lamps,  motors,  electrolytic  cells, 
etc.  Electric  distribution  of  power  is  better  than  other  systems 
on  account  of  its  superior  flexibility,  efficiency,  and  effectiveness ; 
and  we  find  it  taking  the  place  of  other  methods  in  all  but  a  very 
few  applications.  For  some  purposes  the  problem  is  compara- 
tively simple,  while  for  other  uses,  such  as  supplying  a  large 
system  of  incandescent  lamps,  scattered  over  a  comparatively  large 
area,  it  is  quite  complicated.  As  with  other  branches  of  electrical 
engineering,  it  is  only  in  recent  years  that  any  great  advances 
have  been  made  in  the  means  employed  for  transmission  of  elec- 
trical power,  and  wrhile  this  advance  has  been  very  rapid,  there  is 
still  a  large  field  for  development. 

In  a  study  of  this  subject  the  different  methods  employed 
and  their  application,  the  most  efficient  systems  to  be  installed  for 
given  service,  the  preparation  of  conductors  and  the  calculation 
of  their  size,  together  with  the  proper  installation  of  the  same, 
should  be  considered. 

CONDUCTORS. 

Material  Used.  Power,  in  any  appreciable  amount,  is  trans- 
mitted, electrically,  by  the  aid  of  metal  wires,  cables,  tubes,  or  bars. 
The  materials  used  are  iron  or  steel,  copper  and  aluminum.  Other 
metals  may  serve  to  conduct  electricity  but  they  are  not  applied 
to  the  general  transmission  of  energy.  Of  these  three,  the  two 
latter  are  the  most  important,  iron  or  steel  being  used  to  a  consid- 
erable extent  only  iii  the  construction  of  telephone  and  telegraph 
lines,  and  even  here  they  are  rapidly  giving  way  to  copper.  Steel 
may  be  used  in  some  special  cases,  such  as.  extremely  long  spans 
in  overhead  construction  or  for  the  working  conductors  for  rail- 
way installations  using  a  third  rail.  Phosphor  bronze  has  a  lim- 
ited use  on  account  of  its  mechanical  strength. 


POWER  TRANSMISSION 


Copper  and  aluminum  are  used  in  the  commercially  pure  state 
and  are  selected  on  account  of  their  conductivity  and  comparatively 
low  cost.  The  use  of  aluminum  is  at  present  limited  to  long-dis- 
tance transmission  lines  or  to  large  bus-bars,  and  is  selected  on 
account  of  its  being  much  lighter  than  copper.  It  is  not  used  for 
insulated  conductors  because  of  its  comparatively  large  cross-sec- 
tion and  consequent  increase  in  amount  of  insulation  necessary. 

TABLE  I. 
Copper  Wire  Table. 


Dimensions. 


Resistance. 


A.  W.  G. 
or 

B.  &S. 

Diameter. 

Area. 

Ohms  per  foot. 

Inches. 

Circular 
Mils. 

At  20°  C. 

At  50°  C. 

At  80°  C. 

0000 

.460 

211,600 

.00004893 

•.00005467 

.00006058 

000 

.4096 

167,800 

.00006170 

.00006893 

.00007640 

00 

.8648 

133,100 

.00007780 

.00008692 

.00009633 

0 

.3249 

105,500 

.00009811 

.0001096 

.0001215 

1 

.2893 

83,690 

.0001237 

.0001382 

.0001532 

2 

.2576 

66,370 

.0001560 

.0001743 

.0001932 

3 

.2294 

52,630 

.0001967 

.0002198 

.0002435  . 

4 

.2043 

41,740 

.0002480 

.0002771 

.0003071 

5 

.1819 

33,100 

.0003128 

.0003495 

.0003873 

6 

.1620 

26,250 

.0003944 

.0004406 

.0004883 

7 

.1443 

20,820 

.0004973 

.0005556 

.0006158 

8 

.1285 

16,510 

.0006271 

.0007007 

.0007765 

9 

.1144 

13,090 

.0007908 

.0008835 

.0009791 

10 

.1019 

10,380 

.0009972 

.001114 

.001235 

11 

.09074 

8,234 

.001257 

.001405 

.001557 

12 

.08081 

6,530 

.001586 

.001771 

.001963 

13 

.07196 

5,178 

.001999 

.002234 

.002476 

14 

.06408 

4,107 

.002521 

.002817 

.003122 

15 

.05707 

3,257 

.003179 

.003552 

.003936 

10 

.05082 

2,583 

.004009 

.004479 

.0049(54 

17 

.04526 

2,048 

.005055 

.005648 

.006259 

18 

.04030 

1,624 

.006374 

.007122 

.007892 

Resistance.     The   resistance   of  electrical  conductors   is   ex 
pressed  by  the  formula: 

' 


where  R  =  total  resistance  of  the  conductors  considered. 

L  =  length  of  the  conductors  in  the  units  chosen. 
A  =  area  of  the  conductors  in  the  units  chosen. 
f  =  a  constant  depending  on  the  material  used  and  on  the 
units  selected  . 


POWER  TRANSMISSION 


For  cylindrical  conductors,  L  is  usually  expressed  in  feet  and 
A  in  circular  mils.  By  a  circular  mil  is  meant  the  area  of  a  circle 
.001  inches  in  diameter.  A  square  mil  is  the  area  of  a  square 
whose  sides  measure  .001  inches  and  is  equivalent  to  1.27  circular 
mils.  Cylindrical  conductors  are  designated  hy  gauge  number  or 
by  their  diameter.  The  Brown  &  Sharpe  (B.  &  S.)  or  American 
wire  gauge  is  used  almost  universally  and  the  diameters  corre- 
sponding to  the  different  gauge  numbers  are  given  in  Table  I. 
Wires  above  No.  0000.  are  designated  by  their  diameter  or  by 
their  area  in  circular  mils. 

TABLE  II. 
Resistances  of  Pure  Aluminum  Wire. 


A.  W.  G. 
or 
B.  &  S. 

Resistance  at  75^  F. 

R 
Ohms  1,000  ft. 

Ohms  per  mile. 

0000 

.08177 

.43172 

000 

.10310 

.54440 

00 

.13001 

.(58345 

0 

.16385 

.86515 

1 

.20672 

1.09150 

2 

.26077 

1.37637 

8 

.32872 

1.7357 

4 

.41448 

2.1885 

5 

.52268 

2.7597 

6 

.65910 

3.4802 

7 

.83110 

4.3885 

8 

1.06802 

5.5355 

9 

1.32135 

6.9767 

10 

1.66667 

8.8000 

11 

2:1012 

11.0947 

12 

2.6497 

13.9900 

13 

3.3412 

17.642 

14 

4.3180 

22.800 

15 

5.1917 

27.462 

16 

6.6985 

35.368 

17 

8.4472 

44.602 

18 

10.6518 

56.242 

A  convenient  way  of  determining  the  size  of  a  conductor  from 
its  gauge' number  is  to  remember  that  a  number  10  wire  has  a 
diameter  of  nearly  one-tenth  of  an  inch  and  the  cross-section  is 
doubled  for  every  three  sizes  larger  (Nos.  7,  4,  etc.)  and  one-half 
as  great  for  every  three  sizes  smaller  (Nos.  13,  10,  etc.) 


1,000 


6  POWER  TRANSMISSION 

feet  of  number  10  copper  wire  has  a  resistance  of  1  ohm  and 
weighs  31.4  pounds. 

"Wheny  is  expressed  in  terms  of  the  mil  foot,  a  wire  one  foot 
in  length  having  a  cross-section  of  one  mil,  its  value  for  copper  of 
a  purity  known  as  Matthiessen's  Standard,  or  copper  of  100% 
conductivity,  is  9.586  at  0°  C.*  For  aluminum  its  value  is  given 
as  15.2  for  aluminum  99.5%  pure.  Table  II  gives  the  resistance 
of  aluminum  wire. 

This  shows  the  conductivity  of  aluminum  to  be  about  63%  of 
that  of  copper.  The  conductivity  of  iron  wire  is  about  \  that 
of  copper. 

Matthiessen's  standard  is  based  on  the  resistance  of  copper 
supposed,  by  Matthiessen,  to  be  pure.  Since  his  experiments,  im- 
provements in  the  refining  of  copper  have  made  it  possible  to  produce 
copper  of  a  conductivity  exceeding  100%.  Copper  of  a  conductivity 
lower  than  98%  is  seldom  used  f or  power  transmission  purposes. 

Temperature  Coefficient.  The  specific  resistance  (resistance 
per  mil  foot)  is  given  for  copper  as  9.586  at  0°  Centigrade.  Its 
resistance  increases  with  the  temperature  according  to  the  approx- 
imate formula: 

Et  ==  K0  (1   +  at) 

where          Iit  =  Resistance  at  temperature  tf°,  Centigrade. 
R0  -  0J  C. 

a  =  .0042,  commercial  value. 

The  value  of  a  for  aluminum  does  not  differ  greatly  from 
this.  It  is  given  by  Kempe  as  .0039. 

Weight.  The  specific  gravity  of  copper  is  8.89.  The  value 
for  aluminum  is  2.7,  showing  aluminum  to  weigh  .607  times  as 
much  as  copper  for  the  same  conductivity  or  resistance.  It  is  this 
property  wilich  makes  its  use  desirable  in  special  cases.  Iron,  as 
used  for  conductors,  has  a  specific  gravity  of  7.8.  . 

Mechanical  Strength.  Soft-drawn  copper  has  a  tensile 
strength  of  25,000  to  35,000  Ibs.  per  sq.  in.  Hard-drawn  copper 
has  a  tensile  strength  of  50,000  to  70,000  Ibs.  per  sq.  in.,  depending 
on  the  size;  the  lower  value  corresponding  to  Nos.  0000  and  000. 


*The  commercial  values  given  for  the  mil   foot  vary  from  10.7 
to  11  ohms. 


POWER   TRANSMISSION 


Aluminum  Las  a  tensile  strength  of  about  33,000  Ibs.  per  sq. 
in.  for  bard-drawn  wire  ^  incb  in  diameter. 

Effects  of  Resistance.  The  effect  of  resistance  in  conductors 
is  three-fold. 

1.  There  is  a  drop  ju  voltage,  determined  from  Ohm's  law, 

I=-EorE=IB. 

XX 

2.  There  is  a  loss  of  energy  proportional  to  the  resistance  and  the 

TT2 

square  of  the  current  flowing.     Loss  in  watts  =  I2R  =  -^- 

3.  There  is  a  heating  of  the  conductors,  due  to  the  energy  lost,  and 
the  amount  of  heating  allowable  depends  on  the  material  surrounding  the 
conductors.    The  drop  in  voltage  or  the  heating  limit  is  usually  more  im- 
portant in  the  design  of  a  transmission  system  than  the  loss  of  energy. 

Capacity  of  Conductors  for  Carrying  Current.  The  tem- 
perature of  a  conductor  will  rise  until  heat  is  lost  at  a  rate  equal 
to  the  rate  it  is  generated  so  that  a  conductor  is  only  capable  of 
carrying  a  certain  current  with  a  given  allowable  temperature  rise. 
The  limit  of  this  rise  in  temperature  is  determined  by  tire  risk,  or 
injury  to  insulation.  A  general  rule  is  that  the  current  density 
should  not  exceed  1,000  amperes  per  square  inch  of  cross-section 
for  copper  conductors.  This  value  is  too  low  for  small  wire  and 
too  high  for  heavy  conductors,  and  it  is  governed  by  the  way  in 
which  the  conductors  are  installed.  This  value  serves  for  bus-bars 
where  the  thickness  of  the  copper  used  is  limited  to  -J-inch. 
Curves  shown  in  Fig.  1  are  applicable  to  switchboard  wiring,  and 
Table  YII  of  " Electric  Wiring"  gives  safe  carrying  capacity  of 
conductors  for  inside  wiring.  Perrine  gives  the  following  table 
showing  the  class  of  conductors  to  be  used  under  various  conditions: 

TABLE  III. 
Conductors  for  Various  Conditions. 

PART  I. 

Reference  Reference 

No.  Remarks.  No.  Remarks. 

1.  Not  allowed.  8.  In  insulating  tubes. 

2.  Clear  spaces.^  9.  In  wood  moldings. 

3.  Through  trees.  ]().  Without  further  precaution. 

4.  On  glass  insulators.  11.  If  necessary. 

5.  On  porcelain  knobs.  12.  Below  350  volts. 

6.  In  porcelain  cleats.*  13.  Above  350  volts. 

7.  In  wood  cleats^ 


POWER   TRANSMISSION 


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Insulation,  in  the  form  of  a  covering,  is  required  for  elec- 
trical conductors  in  all  cases  with  the  exception  of  switchboard  bus- 
bars and  connections  and  wires  used  on  pole  lines,  and  even  these 
are  often  insulated.  It  may  serve  merely  to  keep  the  wires  from 
making  contact,  as  is  the  case  with  cotton  or  silk-covered  wire. 
Again,  the  wire  may  be  covered  with  a  material  having  a  high 


POWER  TRANSMISSION 


specific  resistance  but  being  weak  mechanically,  and  this  combined 
with  a  material  serving  to  give  the  necessary  strength  to  the  insu- 
lation. For  this  purpose  yarns  are  used  as  the  mechanical  sup- 
port,  and  waxes  and  asphaltum  serve  for  the  insulation  proper. 


Fig-  1. 

Annunciator  wire  is  covered  with  heavy  cotton  yarn  saturated  with 
parath'ne.  The  so-called  Underwriter's  wire  is  insulated  with  cot- 
ton braid  saturated  with  white  paint.  Asphaltum  or  mineral  wax 
is  used  for  insulating  Weatherproof  wire.  It  may  be  applied  in 
several  ways,  the  best  insulation  being  made  by  covering  the  con- 
ductor with  a  single  braiding  laid  over  asphaltum  and  then  passing 


10 


POWER  TRANSMISSION 


the  covered  wire  through  the  liquid  insulation,  at  the  same  time 
applying  two  cotton  braids,  and  finishing  by  an  external  application 
of  asphaltum  and  polishing.  The  most  complete  insulation  is  made 
up  of  a  material  which  gives  the  most  perfect  insulation  and  which 
is  strong  enough,  mechanically,  to  withstand  pressure  and  abrasion 
without  additional  support. 


Fig.  1. 

Qutta  Percha  and  India  Rubber,  Gutta  percha  is  used  for 
submarine  cables,  but  rubber  is  the  insulating  material  most  used 
for  electrical  conductors.  Gutta  percha  cannot  be  used  when  ex- 
posed to  air,  as  it  deteriorates  rapidly  under  such  conditions. 


POWER  TRANSMISSION  11 

Rubber,  when  used,  is  vulcanized,  and  great  care  is  necessary  in 
the  process.  This  vulcanized  rubber  is  usually  covered  with  braid 
having  a  polished  asphaltum  surface.  The  insulation  of  high-tension 
cables  will  be  considered  in  the  topic,  "  Underground  Construction." 

DISTRIBUTION   SYSTEMS. 

Distribution  systems  may  be  divided  into  series  systems,  par- 
allel systems,  or  combinations,  such  as  series-parallel  or  parallel  - 
series  systems.  Various  translating  devices  may  be  connected  in 
circuit,  changing  from  one  system  to  the  other,  and  the  parallel 
system  may  be  divided  into  single  and  multiple-circuit  systems 
commonly  known  as  two-wire  and  three-,  or  Jive-wire  systems. 

Series  Systems  are  applied  to  series  arc  lighting,  series  incan- 
descent lighting,  and  to  constant-current  motors  driving  machin- 
ery, or  generators  feeding  secondary  circuits.  They  serve  for  both 
alternating  and  direct  currents.  Fig.  2  shows  the  arrangement  of 
units  in  this  system.  The  current, 
generated  by  the  dynamo  D,  passes 
from  the  positive  brush  A  (in  direct- 
current  systems)  through  the  units 
L  in  series  to  the  negative  brush  B.  „.  9 

r  ig.  Z. 

For  lighting  purposes,  this  current 

has  a  constant  value  and  special  machines  are  used  for  its  gener- 
ation. The  voltage  at  the  generator  depends  on  the  voltage  required 
by  the  units  and  the  number  of  units  connected  in  service.  As  an 
example,  the  voltage  allowed  for  a  direct-current  open-arc  lamp 
and  its  connections  may  be  taken  as  50  volts.  If  40  lamps  are 
burning,  the  potential  generated  will  be  50  X  40  =  2,000  volts. 
The  number  of  units  is  sometimes  great  enough  to  raise  this  poten- 
tial to  0,000  volts;  but  by  a  special  arrangement  of  the  Brush  arc 
machine,  known  as  the  multiple-circuit  arc  machine,  the  potential 
is  so  distributed  that  its  maximum  value  on  the  line  is  but  2,000 
volts,  provided  the  lamps  are  equally  distributed,  while  the  total 
electromotive  force  generated  is  6,000  volts,  when  the  machine  is 
fully  loaded. 

The  machine  is  supplied  with  three  commutators  and  the 
lamps  connected  as  shown  in  Fig.  3,  which  also  shows  the  distri- 
bution of  potential. 


12 


POWER  TRANSMISSION 


All  calculations  for  series  systems  are  simple.     The  drop  in 

V 

voltage  is  obtained  from  Ohm's  law,  I  =  ~.    A  wire  smaller  than 

No.  8  should  never  be  used  for  line  construction,  as  it  would  not 
be  strong  enough  mechanically,  even  though  the  drop  in  voltage 
with  its  use  should  be  well  within  the  limit. 

The  current  taken  by  arc  lamps  seldom  exceeds  10  amperes. 
For  series  incandescent  lighting,  the  current  may  be  lower  than 


Fig.  3. 

this,  having  a  value  from  2  to  4  amperes.  Special  devices  are  used 
to  prevent  the  breaking  of  a  single  filament  from  putting  out  all  of 
the  lights  in  the  system  and  automatic  short-circuiting  devices  are 
used  writh  series  arc  lamps  for  accomplishing  the  same  purpose. 

As  an  example  of  the  calculation  of  series  circuits,  required 
the  drop  in  voltage  and  loss  of  energy 
in  a  line  four  miles  long  and  composed 
of  No.  8  wire,  when  the  current  flowing 
in  the  line  is  9.6  amperes.  From  Table 
1  we  have  a  resistance  of  .0007007  ohm 
per  foot  for  N"o.  8  wire  at  50°  C.  This 
gives  a  resistance  of  3.7  ohms  per  mile, 
or  a  resistance  of  14.8  ohms  for  the  cir- 
cuit. The  drop  in  voltage  from  Ohm's 
j(1j  4  law  equals  current  times  resistance  or 

equals  9.6  X  14.8  =  142  volts.      The 

loss  in  energy  equals  the  square  of  the  current  times  the  resistance, 
equals  9.62  X  14.8  =  1,364  watts.  If  the  circuit  contains  80  lamps, 
each  taking  50  volts,  the  total  voltage  of  the  system  is  4,142  volts, 

142 

and  the  percentage  drop  in  pressure  is  TTTo  ™  3.43%. 


O 

O 

O 

(0 

z 

o 

1 

\ 

1 

,)JFE.LDERS 

0 

-o 

-0 

POWER  TRANSMISSION  13 

Parallel  Systems  of  Distribution.  In  the  parallel  or  "mul- 
tiple-arc" system  of  distribution,  the  lamps  or  motors  are  supplied 
with  a  constant  potential,  and^the  current  supplied  by  the  generators 
is  the  sum  of  the  currents  taken  by  each  translating  device.  There 
are  several  methods  of  distribution  applicable  to  this  system,  each 
one  having  some  characteristic  which  makes  its  use  desirable  for 
certain  installations.  The  usual  arrangement  is  to  run  conductors 
known  as  "  feeders"  out  from  the  station,  and  connected  to  these 
feeders  are  other  conductors  known  as  mains,  to  which,  in  turn, 
the  receivers  or  translating  devices  are  connected.  *  Fig.  4  is  a 
diagram  of  such  a  "feeder  and  main"  system. 

The  feeders  may  be  connected  at  the  same  ends  of  the  mains, 
known  as  parallel  feeding;  or  they  may  be  connected  at  the  opposite 
ends  of  the  main,  giving  us  the  an  ti  -parallel  system  of  feeding. 
The  mains  may  be  of  uniform  cross-section  throughout,  or  they 
may  change  in  size  so  as  to  keep  the  current  olensity  approximately 
constant.  The  above  conditions  .give  rise  to  four  possible  combi- 
nations, namely  : 

I.  Cylindrical  conductors,  parallel  feeding.    Fig.  5. 

II.  Tapering  conductors,  parallel  feeding.    Fig.  6. 

III.  Cylindrical  conductors,  anti-parallel  feeding.    Fig.  7. 

IV.  Tapering  conductors,  anti-parallel  feeding.    Fig.  8. 

The  regulation  of  the  voltage  of  a  system  is  of  particular  im- 
portance when  incandescent  lamps  are  supplied;  and  the  calcula- 
tion of  the  drop  in  voltage  to  lamps  connected  to  mains  supplied 
with  a  constant  potential  should  be  considered.  Without  going  into 
detail  as  to  the  methods  of  derivation,  we  have  the  following  for- 
mulae which  apply  to  the  above  combinations  when  the  receivers  are 
uniformly  distributed  and  each  taking  the  same  amount  of  current. 
Cylindrical  conductors,  parallel  feeding, 


Tapering  conductors,  parallel  feeding, 

D  =  2  RLr.  II 

Cylindrical  conductors,  anti-parallel  feeding, 

It  I'//'      ,.  TTT 

D=-y-(L-a?)  Ill 

Tapering  conductors,  anti  -parallel  feeding, 

D  =  O.  IV 


14  POWER  TRANSMISSION 

where  D  =  difference  between  potentials  applied  to  different  lamps. 
•R  =  resistance  of  conductors  per  unit  length  at  feeding 
point.  This  will  be  a  constant  quantity  for  cylindrical  conductors, 
but  will  change  for  tapering  conductors,  having  its  minimum  value 
at  the  feeding  point,  and  its  maximum  value  at  the  end  of  the  main. 

I  =  current  in  main  at  feeding  point,  or  point  at  which  the 
feeders  are  connected  to  the  mains.  In  Figs.  5,  6,  7,  and  8  the 
mains  only  are  shown  in  detail. 

ce  =  distance  from  feeding  point  to  the  particular  lamps  at 
which  the  voltage  is  being  considered. 

L  =  length  of  main. 

c> 

For  Cases  I  and  II  the  maximum  difference  of  potential  is 

found  where  %  --  L,  that  is, 
at  the  lamps  located  at"  the 
O>  (|)  (|)  C|)  CJ)  (|)  (|)  (|)      end  of  the  mains. 

For  Case  III  the  maxi- 
mum difference  of  potential 

(j)  (JX^CJ)  (^      is  found,  where  x  ----- ,   or 

Fig.  6.  at  the  lamp  located  at  the 

middle  point  of  the  mains. 


C) 


9  9  9  9  y  9  For  Case  IY  the  potential 

on  all  of  the  lamps  is  the 


Fig.  7.  same,  but  the  difference  be- 

S\  A   A  A  A  A  A  A        tween  the  voltage    on    the 

X  T    T  9  V  V  T  V       feeders  and  the  voltage    on 

'  -  —  '      the  lamps  is  equal  to  RI  L. 

For  unequal  distribution  of 
receivers  and  special  feeding 

points  the  drop  in  voltage  can  be  calculated  by  the  aid  of  Ohm's 
law,  but  this  calculation  becomes  quite  complicated  for  extensive 
systems.  It  usually  is  sufficient  to  keep  the  maximum  drop  writhin 
the  desired  limits  when  designing  electrical  conductors  for  lighting, 
being  careful  not  to  exceed  the  safe  carrying  capacity  of  the  wires. 
The  drop  in  voltage  on  the  feeders  may  be  calculated  directly 
from  Ohm's  law  when  direct  current  is  used,  knowing  the  cur- 
rent flowing  and  the  dimensions  of  the  conductors  used. 


POWER  TRANSMISSION  15 


Additional  formulae  are  given  in  u  Electric  "Wiring,"  whicn 
will  aid  in  determining  the  size  of  wire  to  be  vised  for  a  given 
installation. 

As  examples  of  calculation  we  have  the  following: 
System  consists  of  20  lamps,  each  taking  .5  amperes.     L  =  80 
feet.    R  =  .01  ohm  per  foot  at  feeding  point.    Find  the  maximum 
difference  of  potential  on  the  lamps  in  each  of  the  first  three  cases. 

I  =  20  X  .5  =  =  10  amperes. 

Case  I.         D  =  -Q1  X  10  X  8Q  x   /160  _'80)  =  8  volts. 

oO 

Case  II.       D  =  2  X  .01  X  10  X  80  ==  16  volts. 

.01  X  10  X  -g- 

Case  III.     D  =  —  -.XlSO  -     r)=  2  volts. 

oU  \  &' 

In  Case  IV  the  difference  in  potential  applied  to  the  lamps  and 
the  potential  of  the  feeders  would  be  .01  X  10  X  80  =  8  volts. 

Again,  with  the  maximum  allowable  drop  given,  the  resist- 
ance of  the  wires  at  the  feeding  point  may  be  determined.  For 
tapering  conductors,  the  current  density  is  kept  approximately  con- 
stant by  using  wire  of  a  smaller  diameter  as  the  current  decreases. 
Thus  supposing,  as  in  the  case  considered,  that  the  resistance  at 
the  feeding  point  was  .01  ohm  per  foot.  At  a  distance  of  40  feet 
from  the  feeding  point  the  current  would  be  only  ^  of  10  or  5 
amperes  and  the  size  of  the  wire  would  be  one-half  as  great,  giving 
it  a  resistance  at  this  point  of  .02  ohm  per  foot. 

Feeding  Point,     In  order  to  determine  the  point  at  which  a 
system  of  mains  should  preferably  be  fed,  that  is,  the  point  where 
the  feeders  are  attached  to  the  mains,  it  is  necessary  to  find  the 
electrical  center  of  gravity  of  the  system.     The  method  employed 
is  similar  to  that  used  in  determining  the  best  location  of  a  power 
plant  as  regards  amount  of  copper  required,  and  consists  of  sepa- 
rately obtaining  the  center  of  gravity  of  straight  sections  and  then 
determining  the  total  resultant  and  point  of  application  of   this 
resultant  of  the  straight  sections  to  locate  the  best  point  for  feed 
ing.     Actual  conditions  are  often  such  that  the  system  cannot  be 


16  POWER  TRANSMISSION 


fed  at  a  point  so  determined,  but  it  is  well  to  run  the  feeders  as 
close  to  this  point  as  is  practical,  as  less  copper  is  then  required 
for  a  given  drop  in  potential. 

Consider,  as  an  example,  a  system  such  as  is  shown  in  Fig.  9. 
The  number  of  lamps  and  location  of  the  same  are  shown  in  this 
figure.  The  loads,  ABC  I),  may  be  considered  as  concentrated 
at  A',  a  point  33.8  feet  from  I  arid  equal  to  A  -f-  B  -f  C  +  D. 
This  point  is  obtained  as  follows: 

Kx  =  By.  10  y  =  20  x.  x  +  y  =  400. 
A  +  B  =  30. 
Cx'  =  Dy'.       15^  =  20//.      x'  +  y  =  500.      x  ==  285.7  feet. 

c  +  D  =  35. 

(A  +  B)^  =  (0  +  D)y".     «"  +  ,/'  =  632.4.         __ 
30a?"  =  35y". 

A  +  B  +  C  +  D  =  65 

A'  is  6.2  feet  from  C  or  33.8  feet  from  I. 

E  and  F  may  be  combined  to  form  a  group  of  30  lamps  and 
the  resultant  of  E,  F,  G,  and  II  is  70  lamps  located  at  B',  a  point 
310  feet  from  J,  this  point  being  located  in  the  same  manner  as 
A'.  Similarly  we  find  the  resultant  of  the  loads  at  A'  and  B'  to 
be  135  lamps  located  at  C',  a  point  331.1  feet  from  I,  and  the 
proper  feeding  point  for  the  system. 

A'  =  65  lights,    33.8  feet  from  I. 

B'  =  70  lights,  310  feet  from  J. 

Distance  IJ  =  360  feet. 

Distance  from  A'  to  B'  ==  360  -f  310  -f  33.8  ==  703.8  feet. 


x  -f  y  =  703.8  feet. 

x  =  364.9  feet. 

364.9  -  33.8  ==  331.1  feet. 

The  above  is  a  simple  definite  case.  Should  the  load  be 
variable,  the  proper  feeding  point  will  change  with  the  load,  and, 
in  extensive  systems,  the  location  of  this  point  can  be  obtained 
approximately  only.  The  same  method  of  calculation  is  employed 
in  locating  the  points  from  which  sub-feeders  are  run  out  from- 
the  terminals  of  the  main  feeders  as  is  the  case  in  large  systems, 


POWER  TRANSMISSION 


17 


the  voltage  being  maintained  constant  at  the  point  where  the  sub- 
feeders  are  connected  to  the  feeders. 

Good  practice  shows  the  drop  in  potential  to  be  within   the 

following  limits: 

•*w 
From  feeding  points   (points  where  sub-feeders 

or  mains  are  attached)  to  lamps 5     per  cent. 

Loss  in  sub-feeders o 

Loss  in  mains l.o 

Loss  in  service  wires  . .  .  O.o         " 


The  actual  variation  in  voltage  should  not  exceed  3 


L 


30 


I  A  C 


35 


-y-  - 


Fig.  9. 

In  Series=MultipIe  and  Multiple=Series  Systems,  groups  of 
units,  connected  in  multiple,  are  arranged  in  series  in  the  circuit,  or 
groups  of  units  are  connected  in  series  and  those,  in  turn,  con- 
nected in  multiple,  respectively.  The  application  of  such  systems 
is  limited.  They  are  used  to  some  extent  in  street-lighting  when 
incandescent  lamps  are  used. 


18  POWER  TRANSMISSION 

MULTIPLE=WIRE  SYSTEMS. 

The  Three=Wire  System.  AVe  have  seen  that  in  any  system 
of  conductors  the  power  lost  is  equal  to  PR.  For  a  given  amount 
of  power  transmitted  (IE)  the  current  varies  inversely  with  the 
voltage  and  consequently  the  amount  of  power  lost,  which  is 
directly  proportional  to  the  square  of  the  current,  is  inversely  pro- 
portional to  the  square  of  the  voltage.  Hence,  for  the  same  loss 
of  power  and  the  same  percentage  drop  in  voltage,  doubling  the 
voltage  of  the  system  would  allow  the  resistance  of  the  conductors 
to  be  made  four  times  as  great,  and  wire  of  one-fourth  the  cross- 
section  or  one-fourth  the 
amount  of  copper  would  be 
required.  The  voltage  for 
which  incandescent  lamps, 
Fig.  10.  having  a  reasonable  efficiency, 

can  be  economically  manu- 
factured is  limited  to  220,  while  the  majority  of  them  are  made 
for  110.  In  order  to  increase  the  voltage  on  the  system,  a  special 
connection  of  such  lamps  is  necessary.  The  three-wire  and  five- 
wire  systems  are  adopted  for  the  purpose  of  increasing  this  voltage. 
Fig.  10  shows  a  diagram  of  a  three-wire  system.  Consider  the 
conductor  B  removed,  and  we  have  a  series-multiple  system  with 
two  lamps  in  series.  This  arrangement  does  not  give  independent 
control  of  individual  lamps,  and  the  third  wire  is  introduced  to 
take  care  of  any  unbalancing 

of  the  number  of  lamps  or  A  _^^         _^3      _+a 

units  connected  on  either  side          Q  KJ        •  i(S     i(Si(S 

of  the  system,   and   to  allow      ±  (^   ?  '6'6'cJ)      1616 16 
more  freedom  in  the  location       -    ^_6 
of  the  lights.      The  current  Fig.  11. 

flowing  in   the  conductor  B, 

known  as  the  neutral  conductor,  depends  on  the  difference  of  the 
currents  required  by  the  units  on  the  two  sides  of  the  system. 
Fig.  11  shows  a  system  in  which  the  loads  on  the  two  sides  are 
unequal,  an  unbalanced  system,  with  the  value  of  the  current  in 
the  neutral  wire  at  different  points.  Each  unit  is  here  assumed 
to  take  one  ampere. 


POWER  TRANSMISSION 


19 


0 


9 


As  stated  above,  were  no  neutral  wire  required,  the  amount 
of  copper  necessary  for  a  system  with  the  lamps  connected,  two  in 
series,  for  the  same  percentage  drop  in  voltage  would  be  one-fourth 
the  amount  necessary  for  the  parallel  connection.  This  may  be 
shown  as  follows:  The  current  in  the  wire  in  the  first  case  is  one- 
half  as  great,  so  that  the  voltage  drop  would  be  divided  by  two  for 
the  same  size  wire. 
The  voltage  on  the  sys- 
tem is  twice  as  great, 
so  that,  with  the  same 
percentage  regulation, 
the  actual  voltage  drop 
would  be  doubled. 
Consequently  wire  of 
one-fourth  the  cross - 
section  and  weight  may 
be  used.  If  the  neutral 
wire  is  made  one-half 
the  size  of  the  outside 
conductor,  as  is  usually 
the  case  in  feeders,  the 
amount  of  copper  re- 
quired is  -fft  of  that 
necessary  for  the  two- 
wire  system.  For 
mains  it  is  customary 
to  make  all  three  con- 
ductors the  same  size, 
increasing  the  amount 


G 

Fig.  12. 


of  copper  to  |  of  that  required  for  a  two-wire  system.  For  a  five- 
wire  system  with  all  conductors  the  same  size,  the  weight  of  copper 
necessary  is  .156  times  that  for  a  two-wire  system. 

Multiple-wire  systems  have  no  advantage  other  than  saving 
of  copper,  except  when  used  for  multiple-voltage  systems,  while 
among  their  disadvantages  may  be  mentioned: 

Complication  of  generating  apparatus. 

Complication  of  instruments  and  wiring. 

Liability  to  variation  in  voltage,  due  to  unbalancing  of  load. 


20  POWER  TRANSMISSION 


Fig.  12  shows  some  of  tlie  methods  employed  in  generating 
current  for  a  three-wire  system. 

A.  Two  dynamos  connected  in  series,  the  usual  method 

B.  A  double  dynamo. 

C.  Bridge  arrangement,  using  a  resistance  R  with  the  neutral  con- 
nection arranged  so  as  to  change  the  value  of  resistance  in  either  side  of 
the  system.    Has  the  disadvantage  of  continuous  loss  of  energy  in  R. 

D.  Storage  battery  connected  across  the  line  with  neutral  connected 
at  middle  point. 

E.  Special  dynamo  supplied  with  three  brushes. 

F.  Special  machine  having  collector  rings,  across  which  is  con- 
nected an  impedance  coil,  the  neutral  wire  being  connected  to  the  middle 
point  of  this  coil. 

G.  Compensators  or  motor-generator  set  used  in  connection  with 
generator.  The  motor-generator  set  is  known  as  a  balancer  set. 

Compensators  are  usually  wound  for  about  10%  of  the  capac- 
ity of  the  machine  with  which  they  are  used.  In  the  motor-gen- 
erator set,  one  side  becomes  a  motor  or  generator  depending  on 
whether  the  load  on  that  side  is  less  or  greater  than  the  load  on 
the  opposite  side. 

Voltage  Regulation  of  Parallel  Systems.  It  is  customary  to 
keep  the  voltage  on  the  mains  constant,  or  as  nearly  so  as  possible, 
at  the  point  where  the  feeders  are  attached.  Where  but  one  set 
of  feeders  is- run  out  from  the  station,  this  may  be  readily  accom- 
plished by  the  use  of  over-compounded  dynamos,  adjusted  to  give 
an  increase  of  voltage  equal  to  the  drop  in  the  feeders  at  different 
loads.  Again,  the  field  of  a  shunt-wound  generator  may  be  con- 
trolled by  hand,  the  pressure  at  the  feeding  points  being  indicated 
by  a  voltmeter  connected  to  pilot  wires  running  from  the  feeding 
point  back  to  the  station. 

When  the  system  is  more  extensive,  separate  regulation  of 
different  feeders  is  necessary.  A  variable  resistance  may  be  placed 
in  series  with  separate  feeders,  but  this  is  undesirable  on  account 
of  a  constant  loss  of  energy.  Feeders  may  be  connected  in  along 
a  system  of  mains  and  one  or  more  of  these  switched  in  or  out  of 
service  as  the  load  changes.  Bus-bars  giving  different  voltages 
may  be  aranged  so  that  the  feeders  can  be v  changed  to  a  higher 
voltage  bar  as  the  load  increases.  Boosters — series  dynamos — may 
be  connected  in  series  with  separate  feeders  and  these  may  be  ar- 
ranged to  regulate  the  voltage  automatically.  The  use  of  boosters  is 


POWER  TRANSMISSION 


21 


not  to  be  recommended  except  for  a  few  very  long  feeders,  and  then 
the  total  capacity  of  boosters  should  equal  but  a  small  percentage 
of  the  station  output  if  the  efficiency  of  the  system  as  a  whole  is 
to  remain  high.  Fig.  13  is  a  diagram  of  a  system  using  different 
methods  of  voltage  regulation. 

Alternating=Current  Systems  of  Distribution  may  be  classi- 
fied in  a  manner  similar  to  direct-current  systems,  that  is,  as  series 
and  parallel  systems;  but  in  addition  to  these  we  have  a  classifica- 
tion depending  on  the  number  of  phases  used,  such  as  single-phase, 
quarter-  or  two -phase  and  three-phase  systems. 

The  Series  System  may  consist  of  a  simple  series  circuit  fed 
by  a  constant-current  generator,  or  it  may  be  fed  by  a  constant- 


Fig.  13. 

current  transformer,  the  primary  of  which  is  supplied  with  a  con- 
stant potential,  the  secondary  furnishing  a  constant  current.  For 
a  description  .of  such  a  transformer,  see  "Electric  Lighting". 
Again,  the  current  may  be  maintained  constant  by  means  of  a  con- 
stant-current regulator,  such  as  is  described  in  "Electric  Light- 
ing". Constant-current  alternators  are  seldom  used,  the  two  latter 

C5 

forms  of  regulation  being  applied  to  most  series  installations.  The 
principal  application  of  series  alternating-current  systems  is  to 
street-lighting.  Parallel -series  alternating-current  systems  are 
sometimes  used  for  street-lighting  with  incandescent  lamps. 

Parallel  Systems,  using  alternating  current  are  also  analo- 
gous to  parallel  systems  using  direct  current,  though  the  receivers, 
especially  if  lamps,  are  seldom  connected  directly  to  the  leads  com- 
ing from  the  station,  but  are  fed  from  the  secondaries  of  constant- 

ra 


22  POWER  TRANSMISSION 

potential  transformers,  which  are  connected  to  the  lines  in  parallel, 
and  step  down  the  voltage.  The  readiness  with  which  the  voltage 
of  such  systems  may  be  changed  by  means  of  suitable  transformers 
is  the  chief  advantage  of  the  single-phase  systems.  The  voltage 
may  be  generated  at,  or '  transformed*  up  to,  a"  high  value  at  the 
station,  transmitted  over  a  considerable  distance  over  small  con- 
ductors with  a  small  loss  of  energy,  and  then  transformed  to  the 
desired  value  for  the  connected  units.  Transformers  may  be  readily 
constructed  to  furnish  voltage  for  a  three-wire  secondary  distribu- 
tion. Fig.  14  is  a  diagram  of  a  single-phase  system  supplying 
power  to  both  two-wire  and  three-wire  systems.  Two  separate 
transformers  are  used  for  obtaining  the  three-wire  system,  in  one 
case,  and  a  transformer,  supplied  with  a  tap  connected  to  the  mid- 
dle ppint  of  the  secondary,  is  used  in  the  other  case. 

The  regulation  of  voltage  for  alternating-current  systems  may 
be  accomplished,  as  in  direct -current  installations,  by  means  of 
compounding  ("  composite-  wound  alternators"),  hand  regulation, 
or  resistance  or  reactance  connected  in  series  with  the  feeders.  In 
addition,  the  feeders  may  be  controlled  by  means  of  special  regu- 
lators such  as  the  Stillwell  Regulator,  or  the  "  C  R  "  Regulator, 
which  consist  of  transformers  with  the  primary  coil  connected 
across  the  line  and  the  secondary  in  series  with  the  line,  and  so 
arranged  that  the  number  of  turns  in  one  or  both  windings  may 
be  varied;  other  forms  of  regulators  are  the  magnetic  regulator 
and  the  induction  regulator. 

Polyphase  Systems.  Polyphase  systems  of  distribution  are 
used  where  motors  are  to  be  run  from  the  circuits;  also  for  long- 
distance transmission  lines  partly  on  account  of  the  saving  in  cop- 
per, polyphase  generators  may  be  constructed  more  cheaply,  for 
a  given  output,  than  single-phase  machines  because  of  a  better 
utilization  of  the  winding  space  on  the  armature;  while  single- 
phase  motors,  except  in  small  sizes,  or  series  motors  as  applied  to 
railway  work,  are  not  entirely  satisfactory.  Two-phase  and  three- 
phase  systems  are  the  only  ones  that  are  in  common  use  for  power 
transmission,  three  phases  being  used  for  long-distance  transmis- 
sion lines.  Six  phases  are  used  for  rotary  converters  only,  the 
capacity  of  the  machines  being  greatly  increased  when  connected 
six-phase. 


POWER  TRANSMISSION 


23 


The  amount  of  copper  required  for  the  different  systems, 
assuming  the  weight  of  copper  for  a  single  phase  two- wire  system 
to  be  100%,  is  as  follows: 

Single-phase  two-wire  systems — .100  per  cent 

"          "      three-wire      "        (Neutral  wire  same 

size  as  outside  wires). 37.5 

Two-phase  four-wire  system ; 100 

"        "      three-wire    "       72.9 

Three-phase  three-wire  system 7.5 

11         "       four-wire        "       33.3 

This  assumes  the  voltage  on  the  receivers  to  be  the  same  in 
every  case,  the  maximum  voltage  having  different  values,  depend- 
ing on  the  system  used.     The  three- 
phase  three-wire  system  is  preferable         \ 

to  the   two-phase  three-wire  system         ^ 

for  most  purposes.     In  the    three- 


-O- 
-O 
-O- 


-0-0 
O--O- 
-0-0 
L0L0J 
Fig.  14. 


oo 

00 
00 


Fig.  15. 


phase  four-wire  system  the  maximum  voltage  is  V  3  times  the 
voltage  on  the  receivers.  Were  the  same  maximum  voltage  allow- 
able as  in  the  three-phase  three- wire  system,  the  amount  of  copper 
for  the  three-phase  four-wire  system  would  be  f  that  required  for 
the  three-phase  three-wire  system.  Fig.  15  shows,  diagram  mat  ic- 
ally,  the  connections  of  the  different  systems. 

As  an  example  of  the  way  in  which  the  relative  amounts  of 
copper  are  calculated,  take  the  three-phase  three-wire  system. 
Assume  the  amount  of  power  transmitted  to  be  P  and  the  percent- 


24  POWER  TRANSMISSION 

age  loss  of  energy  to  be^>.  Let  E  =  the  voltage  on  the  receiver, 
I  =  the  current  flowing  in  a  single  conductor,  single-phase  system, 
and  I'  -  -  current  in  a  single  conductor,  three-phase  system.  We 
have  for  the  single-phase  two-wire  system, 

P  ==  IE, 

\ 
for  the  three-phase  three-wire  system, 

P  ==  1/3TE 

IE  =  1/3  PE 
I 


T'     __ 


1/3 


The  loss  in  energy  in  the  two- wire  system  =  j>  P  =  2  PR, 
when  R  =  resistance  of  one  conductor.  The  loss  in  energy  in  the 

three-phase  system  =  ^>  P     -  3  I'2R'. 
Substituting  -    ^  for  I',  we  have 

2  PR  =      ^--°r  2  R  ==  R'- 

The  amount  of  copper  is  inversely  proportional  to  the  resist- 
ance of  the  conductor,  so  that  if  W  -=  weight  of  one  conductor  for 
single-phase  system  and  W  =  weight  of  one  conductor  for  three- 
phase  system,  W  :  =  2  W. 

Two  conductors  are  required  in  the  first  case  =  2  W. 

Three  conductors  are  required  in  the  second  case  =  3  W. 

3  W  ==  .8  W. 

2  W  =  2  W. 

3  W       *  W 
^=2W^^75%- 

TRANSniSSION  LINES. 

Capacity.  Conductors  used  for  the  transmission  of  power 
form,  with  their  metallic  shields,  with  the  ground,  or  with  neigh- 
boring conductors,  condensers,  which,  when  the  line  is  long,  have 
an  appreciable  capacity.  The  capacity  of  circuits  is  quite  readily 
calculated,  the  following  formula  applying  to  individual  cases. 


POWER  TRANSMISSION 


TABLE  IV. 

Capacity  in  nicro=Farads   Per  Mile  of  Circuit  for  Three-Phase 

System. 


Size 
B.  &  S. 

Diain. 
in 
inch. 

Distance 
A 
in  inches. 

Capacity 
C 
in  M.  F. 

Size 
B.  &  S. 

Diain. 
in 
inch. 

Distance 
A 
in  inches. 

Capacity 
in  M.  P. 

0000      .4(>      12 

.0226 

4 

.204 

12 

.01874 

18 

.0204 

18 

.01726 

24 

.01922 

24 

.01636 

48 

.01474 

48 

.01452 

000 

.41 

12 

.0218 

5 

.182 

12 

.01830 

18 

.01992 

18 

.01690 

24 

.01876 

24 

.01602 

48 

.01638 

48 

.01426 

00 

.886 

12 

.0124 

6 

.1(52 

12 

.01788 

18 

.01946 

18 

.01654 

24 

.01832 

24 

.01560 

48 

.01604 

48 

.0140 

0 

.825 

12 

.02078 

7 

.144 

12 

.01746 

18 

.01898 

18 

.01618 

24 

.01642 

24 

.01538 

48 

.01570 

48 

.01374 

1 

.289 

12 

.02022 

8 

.128 

12 

.01708 

18 

.01952 

18 

.01586 

24 

.01748 

24 

.01508 

48 

.0154 

48 

.01350 

•> 

.258 

12 

.01972 

9 

.114 

12 

.01660 

18 

.01818 

18 

.01552 

24 

.01710 

* 

24 

.01478 

48 

.01510 

48 

.01326 

3 

.229 

12 

.01938 

10 

.102 

12 

.01636 

18 

.01766 

18 

.01522 

24 

.01672 

24 

.01452 

48 

.01480 

48 

.01304 

38-88  &  10 


m. 


.  Insulated  cable  with  lead  sheath. 


C  — 


C  = 


38.83  X  10- 

~~4A~ 
JOLT  -__ 

(I 

19.42  >:  10- 
2A 


jle.     Siiigle  conductor  with  earth  return. 


per  mile  of  circuit.    ParaHel  conductors  forming 
a  metallic  circuit. 


26 


POWER  TRANSMISSION 


C  =  Capacity  in    micro-farads.      (Divide   by   1,000,000   to  give 
capacity  in  farads.) 

k    —  specific  inductive  capacity  of  insulating  material   =  1   for 

air  —  2.25  to  3.7  for  rubber. 
D  =  inside  diameter  of  lead  sheath. 
d   =  diameter  of  conductor. 
li    —  distance  of  conductors  above  ground. 
A  =  distance  between  wires. 

Common   logarithms  apply  to   these  formulae   and   C    for   a 
metallic  circuit  is  the  capacity  between  wires. 

TABLE  V. 
Inductance  Per  Mile  of  Three=Phase  Circuit. 


Size 
B.  &S. 

Diameter 
in  inch. 

Distance 
d  in  inches. 

Self-induct- 
ance L. 
henrys. 

Size 
B.  &S. 

Diameter 
in  inch. 

Distance 
d  in  inches. 

Self-induct- 
ance L 
henrys. 

0000 

.46 

12 

'.00234 

4 

.204 

12 

.00280 

18 

.00256 

18 

.00300 

24 

.00270 

24 

.00315 

48 

.00312 

48 

.00358 

000 

.41 

12 

.00241 

5 

.182 

12 

.00286 

18 

.00262 

18 

.00307 

24 

.00277 

24 

.00323 

48 

.00318 

48 

.00356 

00 

.365 

12 

.00248  • 

6 

.162 

12 

.00291 

18 

.00269 

18 

.00313 

24 

.00285 

24 

.00329 

48 

.00330 

48 

-  .00369 

0 

.325 

12 

.00254 

7 

.144 

12 

.00298 

18 

.00276 

18 

.00310 

24 

.00293 

24 

.00336 

48 

.00331 

48 

.00377 

1 

.289 

12 

.00260 

8 

.128 

12 

.00303 

18 

.00281 

18 

.00325 

24 

.00308 

24 

.00341 

48 

.00338 

48 

.00384 

2 

.258 

12 

.00267 

9 

.114 

12 

.00310 

18 

.00288 

18 

.00332 

24 

.00304 

24 

.00348 

48 

.00314 

48 

.00389 

3 

.229 

12 

.00274 

10 

.102 

12 

.00318 

18 

.00294 

18 

.00340 

24 

.00310 

24 

.00355 

48 

.00351 

48 

.00396 

POWER  TRANSMISSION  27 

If  the  capacity  be  taken  between  one  wire  and  the  neutral  point 
of  a  system,  or  the  point  of  zero  potential,  the  capacity  is  given  as: 

C  (in  micro-farads)  =         — ^-r—  per  mile  of  circuit. 


Table  IY  gives  the  capacity,  to  the  neutral  point,  of  different 
size  wire  used  for  three-phase  transmission  lines. 

The  effect  of  this  capacity  is  to  cause  a  charging  current,  90' 
in  advance  of  the  impressed  pressure,  to  flow  in  the  circuit,  and 
the  regulation  of  the  system  is  affected  by  this  charging  current  as 
will  be  seen  later.  Capacity  may  be  reduced  by  increasing  the 
distance  between  conductors  or  in  lead-sheathed  cables,  by  using 
an  insulating  material  having  a  low  specific  inductive  capacity, 
such  as  paper. 

Inductance.  The  self -inductance  of  lines  is  very  readily  cal- 
culated. Following  is  a  formula  applicable  to  copper  or  alumi- 
num conductors: 

L  =  .000558  |~2.303  log  (— )  +  .25]  per  mile  of  circuit  when 

L  =  inductance  of  a  loop  of  a  three  phase  circuit  in  henrys.  The 
inductance  of  a  complete  circuit,  single  phase,  is  equal  to  the 
above  value  multiplied  by  2  -f-  ;/  3. 

Self-inductance  is  reduced  by  decreasing  the  distance  between 
wires  and  it  disappears  entirely  in  concentric  conductors.  Sub- 
dividing the  conductors  decreases  the  drop  in  voltage  due  to  self- 
inductance  but  it  complicates  the  wiring.  Circuits  formed  of 
conductors  twisted  together  have  very  little  inductance.  When 
alternating-current  wires  are  run  in  iron  pipes,  both  wires  of  the 
circuit  must  be  run  in  the  same  pipe,  inasmuch  as  the  self-induc- 
tance depends  on  the  number  of  magnetic  lines  of  force  passing 
between  the  conductors  or  threading  the  circuit,  and  this  number 
will  be  increased  when  iron  is  present  between  the  conductors. 

The  effect  of  self-inductance  in  a  circuit  is  to  cause  the  current 
to  lag  behind  the  impressed  voltage  and  it  also  increases  the  impe- 
dance of  the  circuit. 

The  effect  of  self -inductance  may  be  neutralized  by  capacity 
or  vice-versa.  The  relative  value  of  the  two  must  be  as  follows: 


28 


POWER  TRANSMISSION 


°  ~  (^/)2L 


an(i  L  are  in  farads  and  henrys  respectively, 


•  A 


and/1  is  the  frequency  of  the  system. 

Mutual=Inductance.     By  mutual-inductance  is  meant  the  in- 
ductive effect  one  circuit  has  on  another  sep- 
:      arate    circuit,    generally  a   parallel   circuit   in 
power  transmission.      An  alternating  current 
flowing  in  one  circuit  sets  up  an  electromotive 
force  in  a  parallel  circuit  which  is  opposite  in 
direction  to  the  E.M.F.  impressed  on  the  first 
^    circuit,  and  is  proportional  to  the  number  of 
the  lines  of  force  set  up  by  the  first  circuit 
which  thread  the  second  circuit. 
The  effects  of  mutual  inductance  may  be  reduced  by  increas- 
ing the  distance  between  the  circuits,  the  distance  between  wires 
of  a  circuit  remaining  the  same.     This  is  impractical  beyond  a 


•D 


Pig.  16. 


-«1300fl300  ~«-1 


Upper  cross  arm 


certain  extent,  if  the  circuits  are  to  be  run  on  the  same  pole  line, 
so  that  a  special  arrangement  of  the  conductors  is  necessary. 

Figs.  16  and  17  show  such  special  arrangements.     In  Fig.  10 
AB  forms   the  wires  of  one  circuit  and  CD  the  wires  of  the  other 


POWER  TRANSMISSION  29 


circuit.  Lines  of  force  set  up  by  the  circuit  AB  do  not  thread  the 
circuit  CD,  provided  ABC  and  D  are  arranged  at  the  corners  of 
a  square  so  that  there  is  no  effect  on  the  circuit  CD.  In  Fig.  17 
assume  an  E.M.F.  to  be  set  up  in  the  portion  of  the  circuit  CD  in 
the  direction  of  the  arrows.  The  E.M.F.  in  the  section  DE  will 
then  be  in  the  direction  of  the  arrows  shown  and  the  effects  on  the 
circuit  AB  will  be  neutralized,  provided  the  transposition,  as  the 
crossing  of  the  conductors  is  called,  is  made  at  the  middle  of 
the  line.  Such  transpositions  are  made  at  frequent  intervals  on 
transmission  lines  to  do  away  with  the  effects  of  mutual  inductance 
which,  at  times,  might  be  considerable.  When  several  circuits 
are  run  on  the  same  pole  line,  these  transpositions  must  be  made 
in  such  a  manner  that  each  circuit  is  transposed  in  its  relation  to 
the  other  circuits.  Thus  in  Fig.  17  is  also  shown  the  transposi- 
tion of  the  circuits  of  a  line  composed  of  ten  two-wire  circuits. 

CALCULATION  OF  ALTERNATING=CURRENT  LINES. 

In  dealing  with  alternating  currents,  Ohm's  law  can  be  applied 
only  when  all  of  the  effects  of  inductance  and  capacity  have  been 
eliminated,  and,  since  this  can  seldom  be  accomplished,  a  new  for- 
mula must  be  used  which  takes  such  capacity  and  inductance 
effects  into  account.  Not  only  the  inductance  or  capacity  of  the 
line  itself  must  be  considered,  but  the  nature  of  the  receiver  must 
be  taken  into  account  as  well,  when  the  regulation  of  the  system 
as  a  whole  is  being  considered.  The  following  quantities  must  be 
known  in  the  complete  solution  of  problems  relating  to  alternatintr- 
current  systems. 

1.  Frequency  of  the  current  used. 

2.  Self-induction  and  capacity  of  the  receivers. 

3.  Self-induction  and  capacity  of  the  lines. 

4.  Voltage  of,  and  current  flowing  in,  the  lines. 

5.  Resistance  of  the  various  parts. 

Following  is  a  set  of  formulae  and  an  appropriate  table  for  cal- 
culating transmission  lines  proper  when  using  direct  or  alternating 
current  and  for  frequencies  varying  from  25  to  125,  and  for  single 
and  polyphase  currents.  This  table  is  issued  by  the  General  Elec- 
tric Company. 


30  POWER  TRANSMISSION 

GENERAL  WIRING  FORMULA. 

D  X  W  X  C1 


Area  of  conductor,  Circular  Mils  = 

W  X  T 
Current  in  main  conductors  =  - 


X  E2 


AV  =  Total  watts  delivered. 

D   =  Distance  of  transmission  (one  way)  in  feet. 

j)       -  Loss  in  line  in  per  cent  of  power  delivered,  that  is,  of  AY. 

E    =  Voltage  between  main  conductors  at  receiving  or  con- 
sumer's end  of  circuit. 

For   continuous   current  C'      =   2,160,  T   =   1,  B   =  =   1,  and 
A  ==  6.04. 

X  E  X  B 


ir  n/ 

V  olts  loss  in  lines  = 

Lbs. 


—  —  — 
100 

D2  X  W  X  C"  X  A 
—  x  E.  >(  1)(NK)>fluo 

The  following  formula  will  also  be  found  convenient  for  cal- 
culating the  copper  required  for  long-distance  three-phase  trans- 
mission circuits: 

M2X  K.W.  X  300,000,000 
Lbs.  Copper  —  — 

•  p  X  E' 

M  is  the  distance  of  transmission  in  miles,  K.W.  the  power 
delivered  in  kilowatts,  and  the  power  factor  is  assumed  to  be 
approximately  95%. 

APPLICATION  OF  FORMUL/E. 

"The  value  of  C'  for  any  particular  power  factor  is  obtained  by 
dividing  2,160,  the  value  for  continuous  current,  by  the  square  of 
that  power  factor  for  single-phase,  by  twice  the  square  of  that 
power  factor  for  three-wire  three-phase,  or  four-wire  two-phase. 
The  value  of  B  depends  on  the  size  of  wire,  frequency,  and 
power  factor.  It  is  equal  to  1  for  continuous  current,  and  for 
alternating  current  with  100  per  cent  power  factor  and  sizes  of  wire 
given  in  the  following  table  of  wiring  constants. 

"The  figures  given  are  for  wires  18  inches  apart,  and  are  suffi- 
ciently accurate  for  -all  practical  purposes  provided  the  displacement 
in  pliase  between  current  and  E.M.F.  at  the  receiving  end  is  not 


POWER  TRANSMISSION 


31 


TABLE  VI. 


System. 

Values 
of  A. 

Values  of  C'. 

Per  Cent  Power  Far  tor. 

100 

96 

5)0 

85 

80 

Single-phase        

6.04 
12.08 
9.06 

2,160 
1,080 
1,080 

2,400 
1,200 
1,200 

2,660 
1,880 
1,880 

8,000 
1,500 
1  ,500 

8,880 
1,690 
1,690 

Two-phase  (four-wire)  .... 
Thre-phase  (three-wire)  .  .  . 

System. 

Values  of  T. 

Per  Cent  Power  Factor, 

100 

95 

90 

85 

80 

Single-phase                        

1.00 
.50 

.58 

1.05 
.53 
.61 

1.11 

.55 
.64 

1.17 
.59 

.68 

1.25 
.62 
.72 

Two-phase  (four-wire) 

Three-phase  (three-wire)  

VALUES  OF  B. 

ft 

So 

60  Cycles. 

125  Cycles. 

Per  Cent  Power  Factor. 

Per  Cent  Power  Factor. 

ft* 

95 

90 

85 

80 

95 

90 

85 

80 

0000 
000 

1.62 
1.49 

1.84 
1.66 

1.99 
1.77 

2.09 
1.95 

2.35 

2.08 

2.86 
2.48 

3.24 

2.77 

3.49 
2.94 

00 

1  34 

1.52 

1.60 

1.66 

1.86 

2.18 

2.40 

2.57 

0 

1.31 

1.40 

1.46 

1.49 

1.71 

1.96 

2.13 

2.25 

1 

1.24 

1.30 

1.34 

1.36 

1.56 

1.75 

1.88 

1.97 

2 

1.18 

1.23 

1.25 

1.26 

1.45 

1.60 

1.70 

1.77 

3 

1.14 

1.17 

1.18 

1.17 

1.35 

1.46 

1.53 

1.57 

4 

1.11 

1.12 

1.11 

1.10 

1.27 

1.35 

1.40 

1.43 

5 

1  08 

1.08 

1.06 

1.04 

1.21 

1.27 

1.30 

1.31 

6 

1.05 

1.04 

1.02 

1.00 

1.16 

1.20 

1.21 

1.21 

7 
"  .'       8 

1.03 
1.02 

1.02 
1.00 

1.00 
1.00 

1.00 
1.00 

1.12 
1.09 

1.14 
1.10 

1:14 

1.09 

1.13 
1.07 

9 
10 

1.00 
1.00 

1.00 
1.00 

1.00 
1.00 

1.00 
1.00 

1.06 
1.04 

1.06 
1.03 

1.04 
1.00 

1.02 
1.00 

32 


POWER  TRANSMISSION 


Values  of  B. 

00 

Jg 

o 

e 

0 

1 

"o 

& 

IS 

Per  Cent  Power  Factor. 

8 

££    ££    "ES  •  JS8    88    83    83 

82 

S3    88    S3    S8    88    88    88 

s 

Sis    ggj    £2    gg    gg    88    33 

g 

S5.SS    SS    SS    SS    S8    88 

Per  Cent  Power  Factor. 

S 

^^    Sg    Sg    88    88    83    88 

'eg 

§ 

•  §g?|    S2    §g    83    88    88    88 

g§1    $Sq    SS    §g    88    83    88 

i—  1  rH          rH  1—  I          i—  1  TH          1—  (  i—  1          r-l  i—  1          i—  1  r-l          rH  r—  1 

8 

SS    SS    gJS    S§    gg    88    88 

•suiqo  -0  o<& 
TB  jaajooo'l^d 
8JIAV  jo  90tnnsis8H 

O5  CO         •rfi  1-— 
O5  <M         O5  O2         CO  Ol         C-1  -^         Oi  CC         O  >C         CC 
•^  CD        1^  OS        <M  »O        O  "O        r-  1  O        r-l  CC        i—  I  T-H 
OO         OO         rH  T-H         01  <M         CCf         10  CD         GOO 

T—  1 

•sqi-'lJOOO'l  J3<I 
f)JTAV  a^SI  JocmSpAV 

LO        X  Tt<        -^f  10 

T-HO5         COO         CC  (M         O5CD         OO5         <MO         OlrH 
'sf  O        O  (M        "CO        iO  <M        O  1-        CD  ^O        CC  CC 
CD  »O         "tf<CC         <M<M         rHrH         rH 

SUK  roinoJK) 
a.ii.M.  jo  -eaav 

O1GO        CCCD        CCCD        (MrH        CCCD        OCD        CCO 
rHCD          CCO          OOCO          'O"^1          CCC^I          Oli—  1          rH  i—  I 
(M  rH          rH  rH 

•aSni?£)  -g  sy  -g 
9JIM  jo  -OK 

§O         OO         i—  IC-1         CO  ^         1OCD         i->  00         CiO 
O          O                                                                                                                rH 

very  much. greater  than  that  at  the  generator;  in  other  words,  pro- 
vided that  the  reactance  of  the  line  is  not  excessive  or  the  line 
loss  unusually  high.  For  example,  the  constants  should  not  be 
applied  at  125  cycles  if  the  largest  conductors  are  used  and  the 
loss  20%  or  more  of  the  power  delivered.  At  lower  frequencies, 
however,  the  constants  are  reasonably  correct  even  under  such 
extreme  conditions.  They  represent  about  the  true  values  at  10% 
line  loss,  are  close  enough  at  all  losses  less  than  10%,  ancf  often, 
at  least  for  frequencies  up  to  40  cycles,  close  enough  for  even 
much  larger  losses.  Where  the  conductors  of  a  circuit  are  nearer 
each  other  than  18  inches,  the  volts  loss  will  be  less  than  given  by 


POWER  TRANSMISSION  33 


the  formula?,  and   if  close   together,  as   with  multiple-conductor 
cable,  the  loss  will  be  only  that  due  to  resistance. 

<'•  The  value  of  T  depends  on  the  system  and  power  factor.  It 
is  equal  to  1  for  continuous  current  and  for  single-phase  current 
of  100  per  cent  power  factor.  The  value  of  A  and  the  weights  of 
the  wires  in  the  table  are  based  on  .00000302  pound  as  the  weight 
of  a  foot  of  copper  wire  of  one  circular  mil  area. 

"  In  using  the  above  formulae  and  constants,  it  should  be  particularly 
observed  thatp  stands  for  the  per  cent  loss  in  the  line  of  the  delivered  power, 
not  foi  the  per  cent  loss  in  the  line  of  the  power  at  the  generator;  and  that 
E  is  the  potential  at  the  delivery  end  of  the  line  and  not  at  the  generator. 

"  When  the  power  factor  cannot  be  more  accurately  determined 
it  may  be  assumed  to  be  as  follows  for  any  alternating  system  oper- 
ating under  average  conditions:  Incandescent  lighting  and  syn- 
chronous motors,  95%;  lighting  and  induction  motors  together, 
85%;  induction  motors  alone,  80%. 

"  In  continuous -cur  rent  three-wire  systems,  the  neutral  wire  for 
feeders  should  be  made  of  one- third  the  section  obtained  by  the  for- 
mulas for  either  of  the  outside  wires.  In  both  continuous  and  alter- 
nating-current systems,  the  neutral  conductor  for  secondary  mains 
and  house  wiring  should  be  taken  as  large  as  the  other  conductors. 

u  The  three  wires  of  a  three-phase  circuit  and  the  four  wires  of 
a  two-phase  circuit  should  all  be  made  the  same  size,  and  each 
conductor  should  be  of  the  cross-section  given  by  the  first  formula". 

Numerical  examples  of  the  application  of  this  table,  as  well 
as  of  other  formulae,  are  given  later. 

A  better  idea  of  the  way  in  which  the  different  quantities  in- 
volved affect  the  regulation  of  an  alternating-current  line  may  be 
obtained  from  graphical  representation  or  from  formulae  which  are 
not  so  empirical.  Before  taking  up  other  methods  of  calculation, 
however,  let  us  consider  the  meaning  of  power  factor. 

By  power  factor  we  mean  the  cosine  of  the  angle  by  which 
the  current  lags  behind  or  leads  the  electromotive  force  producing 
that  current.  It  is  the  factor  by  which  the  apparent  watts  (volts 
times  amperes)  must  be  multiplied  to  give  true  power.  The  formula 
for  po\ver  in  a  single-phase  circuit  is  then, 

Power  =  IE  cos  0  when  6  is  the  lag  or  lead  angle;  and  for 
three-phase  circuits, 


34  POWER  TRANSMISSION 

Power  ==  IE  cos  0  V  3  when  I  is  the  current  flowing  in  a 
single  conductor. 

For  two-phase  circuits,  balanced  load,  this  "becomes, 

Power  =  2  IE  cos  0;  and, 

Power  =  2  1/3  IE  cos  0,  for  six-phase  circuits. 

For  single  and  three-phase  circuits  E  is  the  voltage  between 
lines.  For  two-phase  circuits  it  is  the  voltage  across  either  phase, 
and  for  six-phase  circuits  it  is  the  voltage  across  one  phase  of  what 
corresponds  to  a  three-phase  connection. 

Considering  the  formula  for  single  phase,  we  find  that  the 
current  flowing  in  the  line  may  be  taken  as  made  up  of  two  com. 
ponents,  one  in  phase  with  the  voltage  and  one  90°  out  of  phase, 
lagging,  or  leading,  depending  on  conditions.  In  Fig.  18  let  OE 

equal  the  impressed  pres- 
sure and  OC  the  current 
flowing.  6  =  angle  of  lag. 
The  current  OC  may  be 
resolved  into  two  compo- 
nents, one  in  phase  with 
OE  =  OB,  and  one  90  de- 
grees behind  OE  =  BC. 

OB  =  OC  cos  6  and  is  known  as  the  active  component  of  the 
current. 

BC  =  OC  sin  0  and  is  known  as  the  wattless  component  of 
the  current. 

The  capacity  and  inductance  are  distributed  throughout  the 
line,  that  is,  the  line  may  be  considered  as  made  up  of  tiny  con- 

j— — ^OTiP — I — n^Tt — I — nrftp — I — nnp — i — IWF — i — ifflp — i — <IRR^ — \ 

O      1      ll      1      111     If       1:1 

2= — — nm^ — I — nffln — ' — -^w^ — ' — nmp — I — nnn^J oj^p — I — ^^ — I 

Fig.  19. 

densers  and  reactance  coils,  connected  at  short  intervals  as  shown 
in  Fig.  19.  Considering  the  inductance  and  capacity  as  distributed 
in  this  manner,  the  regulation  of  a  syistem  may  be  calculated,  but 
the  process  is  very  difficult,  and  simpler  methods,  which  give  very 
close  results,  have  been  adopted  for  practical  work.  Probably  the 


POWER  TRANSMISSION  35 

methods  presented  by  Perrine  and  Baum  are  as  simple  as  any  ex- 
cept  those  based  on  purely  empirical  'formulae. 

Tables  giving  the  capacity  and  inductance  of  lines,  together 
with  the  formulae  for  the  calculation  of  these  quantities,  have 
already  been  given.  It  has  also  been  stated  that  the  effect  of  the 
capacity  of  a  line  is  to  cause  a  charging  current  to  flow  in  the  line, 
this  current  being  90°  in  advance  of  the  impressed  voltage.  The 
value  of  this  charging  current  i-s: 

Charging  current  per  wire  =  Z,  single-phase. 

C  =  capacity  in  micro-farads  of  one  wire  to  neutral  point. 
f  =  frequency  o£  the  circuit. 
E  =  voltage  between  wires. 

9 

Charging  current,  three-phase,  =          r  or  1.155  X  charging 

1/3 

current,  single-phase. 

Since  the  voltage  across  the  lines  is  not  the  same  all  along 
the  line,  the  value  of  the  charging  current  will  not  be  the  same, 
but  the  error  introduced  by  assuming  it  to  be  constant  is  not  great. 
For  our  calculation,  then,  we  assume  that  the  charging  current  in 
an  open-circuited  line  is  constant  throughout  its  length,  and  also 
that  the  capacity  of  the  line  may  be  taken  as  concentrated  at  the 
center  of  the  line. 

R 


Fig.  20. 

Consider  a  single-phase  line  such  as  is  shown  diagrammatically 
in  Fig.  20. 

Let  EO  =  the  voltage  at  the  generator  end  of  the  line. 
E    =  the- voltage  at  the  receiver. 
L    =  self  induction  of  the  line. 
Ic   =  charging  current  per  wire. 

I     =  current  flowing  in  the  line  due  to  the  load  on  the 
line. 


36  POWER  TRANSMISSION 

6    =  angle  by  which  the  load  current  differs  frOm  the 

impressed  voltage. 
R   —  resistance  of  the  line. 
e    =  drop  in  voltage  in  the  line. 

w     —    2  77  f. 

+  ,;'  is  a  symbol  indicating  that  the  current  is  90°  in 

advance  of  the  pressure. 
-j  indicates  that  the  current  is  90°  behind  the  pressure. 

The  expression,  1/R2  +  (2  7T/L)2  =  1/R2  +  <ya  L2  may  be 
represented  by  R  +  ^'L  &>,  the  factor  -f  ,/  indicating  that  the  square 
root  of  the  sum  of  the  squares  of  these  two  quantities  must  be 
taken  to  obtain  the  numerical  result.  The  quantity/2  may  be  con- 
sidered as  -  1. 

Taking  the  capacity  of  the  line  and  considering  it  as  a  con- 
denser located  at  the  middle  of  the  line,  we  may  assume  the  charg- 
ing current  as  flowing  over  only  one-half  of  the  line,  or  one-half  the 
charging  current  may  be  considered  as  flowing  over  all  of  the  line. 

The  im-pedance  of  the  line  is  equal  to  1/R2  -f-  co2  L2  =  R  -j-  jLw. 
The  power  factor  of  the  load  =  cos  6. 
The  active  component  of  the  current  is  I  cos  6. 
The  wattless  component  of  the  current  is  -jl  sin  6  (-j  indicat- 
ing that  the  current  lags  90°  behind  the  pressure). 

The  charging  current  may  be  represented  by  -f  j  ~j~- 

Then  the  drop  due  to  the  active  component  of  the  load  is 

I  cos  6  (K  +  fLo>). 

The  drop  due  to  the  wattless  component  of  the  load  is 
-jl  sin  0(R  -h/Lcu). 

The  drop  due  to  the  charging  current  is  +  j-jj~(R  +/L®) 

The  total  drop  is  equal  to  the  sum  of  these  three  values  =  0, 
so  that, 

Eo  =  E  +  e  =  I  cos  9  (R  +  jLu)  -jl  sin  6  (R  + 


Expanding  this  and  substituting  -  1  for/2  we  have, 


POWER  TRANSMISSION 


37 


E0  =  E  +  I  cos  6  R  -f  jl  cos  0  Lo>  -jl  sin  0  R  +  I  sin  6  Lo> 


Referring  to  Fig.  21  \ve  have  these  various  values  plotted 
graphically. 

.  ICR  IpL<y 

oa  =  E,  aJ  =  -j  -_-,  fo  =  - 


—  -f-  ./I  cos  6  Lw, 

sin  # 


cd  =  -f-  I  cos  #  R? 

ef  =  —  ^'IR  sin  0, 

off  =  E0. 

«J  is  plotted  90°  in  advance  of  oa  on  account  of  the  symbol 

Jc  is  plotted  in  the  opposite  direction  from  oa  on  account  of 
the  negative  sign. 

ef  is  plotted  downward  on  account  of  the  symbol  —j. 


"xi* 
Fig.  21. 

If  we  let  oa',  Fig.  21,  represent  the  current  vector,  then  6  = 
angle  of  lag,  and  eg  which  equals  IR  is  plotted  parallel  to  oa'  and 
ce  =  ILw  is  plotted  perpendicular  to  oa'. 

It  is  seen  from  this  that  the  charging  current  tends  to  pro- 
duce a  rise  in  E.M.F.  instead 'of  a  drop  in  pressure. 

The  above  takes  into  account  only  the  constants  of  the  line. 
In  order  to  determine  the  regulation  of  a  complete  system,  the 


38  POWER  TRANSMISSION 

resistance,  capacity,  and  inductance  of  the  translating  devices  must 
be  considered  as  well.  In  Fig.  22  is  shown  a  diagram  of  a  com- 
plete system  with  both  step-up  and  step-down  transformers  con- 
nected in  service.  The  charging  current  may  be  considered  as 
flowing  through  half  of  the  system  only,  namely,  the  generator, 
the  step- up  transformers,  and  one -half  of  the  line. 

L    R 


Fig.  22 

Let  Kj  =  the  equivalent  resistance  of  the  step-down  trans- 
formers. 

B2  =  the  equivalent  resistance  of  the  step-up  trans- 
formers. 

Lj  =  inductance  of  the  step-down  transformers. 

L2  =  inductance  of  the  step-up  transformers. 

Kg  =  equivalent  resistance  of  the  generators. 

Lg  =  equivalent  inductance  of  the  generators. 

R   =  resistance  of  the  line. 

L   =  inductance  of  the  line. 

1*=!^  +  L2  +  Lg  +  L. 

KT  =  Ps  +  E2  +  Eg  +  R. 

All  quantities  should  be  converted  into  their  equivalent 
values  for  the  full  line  pressure.  Thus  the  generator  and  re- 
ceiver voltages  should  be  multiplied  by  the  ratio  of  transforma- 
tion of  the  step- up  and  step-down  transformers,  respectively,  to 
change  them  to  the  full  line  pressure.  The  resistance  and  induc- 
tance of  the  transformers  must  include  the  resistance  and  inductance 
of  both  windings,  and  the  value  must  correspond  to  the  line  voltage. 
Thus  the  resistance  of  the  step- up  transformers  will  be  i\  n2  -f-  7*2, 

when  rt  =  resistance  of  primary  coil, 
r2  =  resistance  of  secondary  coil, 
11  =  the  ratio  of  transformation.      In  the  same  way,  the 

equivalent  resistance  of  the  step-down  transformers  will  be  ^-f-  n2 
rr     The  generator  resistance  and  inductance  must  be  multiplied  by 


to  bring  them  to  equivalent  values  for  the  full  line  pressure. 


POWER  TRANSMISSION  39 

Our  formula  then  becomes:  — 

E0  ==  E  +  I  cos  e  (KT  +JLTo>)  -j  I  sin  0  (KT  +  t/LTo>)  + 

*  l*   [(I  +  **  +  Es)  +>  (t  +  L>  + 

Plotted  graphically  we  have,  Fig.  21: 

6»t£  —   E  6Y/  =    I  COS  0  Km 

de  =     I  cos  0  L 


The  numerical  value  of  E  and  E0  may  be  determined,  from  a 
diagram  such  as  is  shown  in  Fig.  21,  wThen  constructed  to  scale; 
or  it  may  be  calculated  analytically,  remembering  that  the  quan- 
tities affected  by  j  are  to  be  combined,  geometrically,  with  the 
quantities  not  affected  by  the  symbol. 

The  above  formulae  apply  to  single-phase  circuits  directly. 
If  to  be  used  for  the  calculation  of  three-phase  circuits,  the  follow- 
ing points  must  be  .observed: 


1.    Charging  current  (  Ic  )  three-phase  =      ,—   x  charging  current 

v  o 

single-phase. 

'2.  The  voltage  should,  preferably,  be  considered  as  the  voltage  be- 
tween one  line  aud  the  neutral  point.  The  voltage  to  the  neutral  point 
will  be  the  line  voltage  divided  by  ]/  3. 

3.  The  resistance  of  one  line  only  is  considered,  not  the  resistance 
of  a  loop. 

4.  The  inductance  of  one  line  only  is  used.    The  inductance  of  one 
line  equals  the  inductance  of  a  loop  divided  by  j/j£ 

Examples  of  AIternating=Current  Line  Calculation. 

1.  What  is  the  capacity,  in  micro-farads,  between  wires  of  a 
single-phase  transmission  line  10  miles  in  length  composed  of 
number  6  copper  wire  spaced  15  inches  apart  ?  AVhat  is  the 
capacity  to  the  neutral  point  ? 

19  42  X   10"9 
(J  in  farads  =  -^  --  per  mile  of  circuit. 

,  £  A. 

log   -j 

A    =15'  inches  d  --  .1<>2  inches.    . 

9  \ 

~'      =185  log  185  ==  2.2072 

Co 


40  POWER  TRANSMISSION 


19  4^  y  10~9 

0  in  farads  =  -   '  "  :          -  X  10  -  .000000085 


4. 

C  in  micro-farads  =  .000000085  X  1,000,000  ==  .085 

r\  Wt+J  /> 

0  in  micro-farads  with  respect  to  the  neutral  point  —   -        - 


/\^V  W/> 

C  iii  micro-farads  —  o  ^ 


This  shows  that  the  capacity  to  the  neutral   point  is  twice  the 
capacity  to  the  other  wire. 

2.     What  is  the  self  inductance  of  the  above  circuit  ? 

>er  mile  of 


L  =  .000558  X  -=f  2.303  log  -T  -f  /*„  , 

I/  3  \  '    d  )  circuit. 

L  =  .000644  (2.303  X  2.2672  +  .25)  X  10 
-  .000644  X  5.47  X  10  =  .0352  henrys. 

3.     A  circuit  has  a  capacity  of  .2  micro-farads.     What  must 
be  the  value  of  its  inductance  to  compensate  for  this  capacity  at 

60  cycles  ? 


C  =  .0000002  farads 

(27T/7  =  (2  X  3.1416  X  CO/  ==  142122 

-0000002  = 


L  =  1  -5-  (142122  X  0000002)  ===  35.2  lienrys 

4.  It  is  desired  to  transmit  1,000  K.W.  a  distance  of  25 
miles  at  a  voltage  of  20,000,  a  frequency  of  60  cycles,  and  a  power 
factor  of  85%.  Transmission  is  to  be  a  three-phase  three-wire  sys- 
tem. Allowing  10%  loss  of  delivered  power  in  the  line,  required: 

a  Area  of  cond  uctor. 

b  Current  in  each  conductor. 

c  Volts  lost  in  line. 

d  Pounds  of  copper. 

1)  X  W  X  C' 


Circular  mils  = 


— 
p  X  E 


D  =  25  X  5,280  ==  132,000 

W  =  1,000  X  1,000  =±  1,000,000 


POWER  TRANSMISSION  41 

C'     =  1,500  for  three-phase  three  wire  system  and  85%  power 
factor. 

p  =  =  10 

E  ==  20,000     E2  =  =  400,000,000 

132000  X  1000000  X  1500 


Circular  mils  = 


=  49,500. 

Number  8  wire  has  a  cross-section  of  52,400  cir.  mils. 

W  X  T 
b     Current  in  each  conductor  =  --  ~  —       =  34. 

T  =  .68  for  three-phase  system,  85%  power  factor. 

•^  ,  p  X  E  X  B 

c     v  olts  lost  in  line  =  -  —  ^-  — 

B  =  1.18  for  number  3   wires,  60  cycles   and   85%    power 
factor. 

10  X  20,000  X  1.18 

Volts  lost  =  -  -  =  23(50 

1UU 

D3  x  W  X  C-  X  A 

*>pp«  =     -;  or  ]t  ma  be  cal- 


culated  directly  from  the  weight  of  wire  given  in  the  tables  after 
the  size  of  wire  has  been  determined  by  other  formulae.  Thus  75 
miles  of  number  3  wire  is  required.  This  weighs  159  pounds 
per  1,000  feet. 

159  X  5.280  X  75  ==  62,964  pounds. 

5.  A  single-phase  line  20  miles  in  length  is  constructed  of 
number  000  wire  strung  24  inches  apart.  It  is  desired  to  trans- 
mit 500  K.W.  over  this  line  at  a  frequency  of  25  cycles  and  a 
power  factor  of  80%,  the  voltage  at  the  receiver  end  being  25,000. 
Considering  the  line  drop  only,  what  must  be  the  voltage  at  the 
generator  end  of  the  line? 

E0  =  E  +  I  cos  -0  II  +  j  I  cos  eisto—jl  sin  0  II  +  I  sin  0 


T  •        J  p        ~l  ^  1  f »        -W- 

A     ft)      -}-    J     -~         K     —    •  1--     ft). 

>5     (Power  ==  IE  cos  0) 


E    =:  25,000 

500,000 


25,000  X  .80 


42  POWER  TRANSMISSION 

Cos  6  =  .80 

Sin  0  =  .60  (from  trigonometric  tables) 

R  =  resistance   of   40    miles  of  number  000  wire  =  14.56 
ohms  at  50°  C. 

L  =  .00277  X  ~L  X  20  =  .064  (calculated  from  Table  V). 

a>-=2'nf=  27rX  25  =  157 

E  X  C  X  2  TT  X-/      25,000  X  .3752  X  157 
ic "  2  X  10«  2  x  1,000,000 

C  =  .3752  (Table  IV  or  calculated). 

Substituting  these  values  in  the  above  formula  we  have, 
E0  =  25,000  +  291.2  +j  200.8  -j 218.4  -f  150.6  -f  e/5.36  -  8.7 
E0  =  25,000  -f  291.2  +  150.6  -'3.7  +  j  (200.8  -  218  4  +  5.36) 
E0  =  25,000  +  291.2  +  150.6  -  3.7  -j  (218.4  -  200.8  -  5.36) 


E0  =  V (25,000  +  291.2  +  150.6  -  3.7)2  -f  (218.4  -  200.8  -  5  36)2 
Since  the  symbol  j  indicates  that  the  quantities  must  be  com- 
bined geometrically. 

E0  =  l/(25;438.1)2  +  (12.24)2  —  25,438.1  volts. 

6.  A  three-phase  line  20  miles  in  length  is  constructed  of 
number  000  wire  strung  24  inches  apart.  We  wish  to  transmit 
1,000  K.W.  over  this  line  at  a  frequency  of  25  cycles  and  a  power 
factor  of  85%,  the  voltage  at  the  receiving  end  being  2,000.  Three 
Y-connected  500  K.W.  transformers  having  a  ratio  of  10  :  1  step 
the  voltage  up  and  down  at  either  end  of  the  line.  The  resistance 
of  the  high-tension  winding  of  each  transformer  is  4  ohms.  The 
resistance  of  the  low-tension  windings  is  .04  ohms.  The  induc- 
tance of  each  transformer  is  4  henrys.  Neglecting  the  generator 
constants,  what  must  be  the  voltage  applied  to  the  low-tension 
windings  of  the  step-up  transformers? 

E0  =  E  +  I  cos  6  (RT  +  j LTe»)  -jl  sin  0  (KT  -J-  j LTo>)  -f  j Ic 


Since  this  is  for  a  three-phase  circuit  we  will  work  with  the 
voltage  to  the  neutral  'point  and  will  change  all  values  to  corre- 
spond to  the  line  voltage.  Hence, 


POWER  TRANSMISSION  43 


,  x  10  =       x  10  + 

1/3  V  3 


1  —  34  amperes.  Since  1    3  IE  Cos  6  --  1.000,000 

E  =--  10  X  2,000  ==  20,000 
Cos  6  =  .85 
I  —  34. 

IIT  ==  Resistance  of  one  line  +  equivalent  resistance  of  one 
transformer  at  each  end  of  the  line. 

KT  =  7.28  ohms  +  4  +  100  X  .04  +  4  +  100  >(  .04. 

=  23.28  ohms. 

LT  =  .0554  -*•  1/3"+  .4  +  .4  ==  .832  henrys. 
o>  ==  157 

sin  6  =  .52 

2 
Ic  =  .589   X   -        =  .(377  amp.  =  charging  current  single- 

2 
])hase  X  - 

1/3 

R      ^  PA  . 

-y  =  3.64 

It,  =='  8 

^  —  .010  L2  =  .4 

Hubstituthig  these  values  in  our  formula  we  have, 


+  ^'7.88-44.2 
=  11,550  +  672.8  +  2,309-44.2  +  j  (3,774  -  411.6  +  7.88) 

--  V  14,487.^  +  3370.32  ==  14,874 
£0  =  2,573  volts. 


TRANSFORMERS. 


A  transformer  consists  of  two  coils  made  up  of  insulated  wire, 
the  coils  being  insulated  from  each  other  and  from  a  core,  made 
up  of  laminated  iron,  on  which  they  are  placed.  One  of  these 
coils,  known  as  the  primary  coil,  is  connected  across  the  circuit,  in 
constant-potential  transformers,  and  the  other  coil,  known  as  the 


44  POWER  TRANSMISSION 

secondary  coil,  is  connected  to  the  lamps  or  motors,  or  whatever 
makes  up  the  receivers.  As  a  matter  of  fact,  these  coils  are  each 
usually  made  up  of  several  sections.  The  voltage  induced  in  the 
secondary  windings  is  equal  to  the  voltage  impressed  on  the  pri- 
mary winding  multiplied  by  the  ratio  of  the  number  of  turns  in 
the  secondary  to  the  number  in  the  primary  coil,  less  a  certain  drop 
due  to  impedance  of  the  coils  and  to  magnetic  leakage.  This  drop 
is  negligible  on  no  load.  If  transformers  are  used  to  raise  the 
voltage,  they  are  termed  step -up  transformers.  If  used  to  lower 
the  voltage,  they  are  called  step-down  transformers. 

Losses  of  power  occurring  in  transformers  are  of  two  kinds 
namely: 

Iron  or  core  losses  which  are  made  up  of  hysteresis  and  eddy- 
current  losses  in  the  iron  making  up  the  core,  and 

Copper  losses  which  are  due  to  the  I2R  losses  in  the  windings 
with  the  addition,  in  some  cases,  of  eddy  currents  set  up  in  the 
conductors  themselves. 

The  efficiency  of  a  transformer  depends  on  the  value  of  these 
losses  and  may  be  expressed  as  the  ratio  of  the  watts  output  to 
the  watts  input. 

W,       W..-IW,  +  Wh  +  We) 

WP  "  Wp 

"W"s  =  watts  secondary. 
Wp  =  watts  primary. 
Wc  =  copper  losses. 
Wh  =  hysteresis  losses. 
We  =  eddy  current  losses. 

The  iron  losses  remain  constant  for  any  given  voltage  regard- 
less of  the  load,  while  the  copper  losses  are  proportional  to  the 
square  of  the  current.  The  efficiencies  of  transformers  are  high, 
varying  from  94  to  95%  at  ^  load  to  98%  at  full  load  for  sizes 
above  25  K.W. 

By  All=Day  Efficiency  is  meant  the  efficiency  of  a  trans- 
former, taking  into  consideration  its  operation  for  twenty. four 
hours,  and  it  is  calculated  for  the  ratio  of  watt-hours  output  to 
watt-hours  input  for  this  length  of  time  when  in  actual  service. 
For  calculation,  the  transformer  is  often  assumed  to  be  fully  loaded 


POWER  TRANSMISSION 


45 


WWWWW 


vVv        VWWWWv 


nwVWWAM       ^WWWWVj 
I 


for  five  hours  and  run  with  no  load  for  the  remaining  nineteen. 
The  all-day  efficiency  is  then  determined  as  follows: 

Output,  K.W.  hours  ==  watts  output  at  full  load  X  5. 
Input,  K.W.  hours    :  =  watts  output  at  full  load  X  5  +  12E 
loss  at  full  load  X  5  -f  core  loss  at  normal  voltage  X  24. 

A11   ,.       «,  .  output,  watt-hours 

All-day  efficiency  =  -. — i- — 

input,   watt-hours. 

The  assumption  that  a  lighting  transformer  is  fully  loaded 
five  hours  out  of  the  day  is  not  always  a  correct  one.  On  many 
circuits  from  two  to  three  hours  of  full  load  would  be  more  nearly 
the  proper  value  to  use  in  calculating  the  all-day  efficiency. 

By  Regulation  of  a  transformer 
is  meant  the  percentage  drop  in  the 
secondary  voltage  from  no  load  to  full 
load  when  normal  pressure  is  im- 
pressed on  the  primary.  This  drop  is 
due  to  the  IH  drop  in  the  windings 
and  to  magnetic  leakage.  In  well 
designed  transformers  the  loss  due  to 
magnetic  leakage  is  about  10%,  or 
less,  of  that  due  to  the  resistance  drop. 
For  non-inductive  load  (power  factor 
=  unity)  the  regulation  is  from  1  to 
3%  in  good  transformers.  With  in- 
duction load  this  is  increased  co  4  or 
5%,  or  even  more.  p.  oo 

Both  the  efficiency  and  the  reg- 
ulation should  be  considered  in  selecting  a  transformer  for  given 
service.  Thus,  if  a  transformer  is  to  be  used  for  lighting,  its  reg- 
ulation should  be  of  the  best,  since  drop  in  voltage  due  to  the  trans- 
former is  in  addition  to  that  due  to  the  conductors.  In  the  same 
way  the  regulation  of  any  system  as  a  whole  depends  to  a  certain 
extent  on  the  regulation  of  the  transformer  installed. 

If  the  efficiency  of  a  transformer  is  low,  it  means  a  direct  loss 
of  considerable  energy  as  well  as  greater  heating  of  the  transformer 
and  consequent  deterioration.  If  a  transformer  is  to  be  used  for 
lighting  purposes,  or  is  lightly  loaded,  a  large  portion  of  the  time, 


POWER   TRANSMISSION 


a  type  should  be  selected  which  has  a  relatively  low  core  loss  so  as 
to  increase  the  all-day  efficiency.  If  fully  loaded  "all  day,  the 
losses  should  be  divided  about  equally  between  the  copper  and  the 
iron  losses. 

Transformer  Connections.  Transformers  for  three-phase 
work  may  be  connected  in  two  ways.  Where  three  transformers 
are  used,  they  may  be  connected  in  Y  or  star,  that  is,  with  one 
terminal  of  each  primary  brought  to  a  common  point  and  the  other 

terminal  connected  to  a  line  wire 
(see  Fig.  23),  or  they  may  be  con- 
nected in  A  or  mesh  when  the  three 
primaries  are  connected  in  series  and 
the  line  wires  are  connected  to  the 
three  corners  of  the.  triangle  so 
formed  (see  Fig.  24).  The  second- 
aries may  be  connected  in  Y  the 
same  as  the  primaries  or  the  second- 
aries may  be  connected  in  Y  when 
the  primaries  are  in  A,  or  vice  versa. 
The  voltage  relation  may  be  best  de- 
termined from  vector  diagrams  as 
shown  in  Fig.  25,  which  gives  the 
voltage  relation  of  step-down  trans- 
when  the  voltage  across  the  primary 


WvA^AAA^V~^\A/\AAAA^AAAT-*-\^\AWAAAA' 
^WAVWWj       N/VWWWVVM      ^/VWVWWM 


Fig.  24. 


formers  with  a  ratio  of  10 
lines  is  1,000, 

Changes  may  be  made  from  two  to  three  phases,  or  from  three 
to  two  phases,  with  or  without  a  change  of  voltage,  by  means  of 
transformers  having  the  required  ratio  of  transformation  by  use  of 
what  is  known  as  the  Scott  connections.  Fig.  26  shows  such  a 
connection  together  with  a  corresponding  vector  diagram  showing 
the  relations  when  the  change  is  from  two  to  three-phase  with  a 
10  :  1  transformation  of  voltage.  The  main  transformer  is  fitted 
with  a  tap  at  the  middle  point  of  the  secondary  wiring  to  which 
one  terminal  of  the  teaser  transformer  is  connected.  The  teaser 
has  a  ratio  of  transformation  differing  from  that  of  the  main  trans- 
former, as  shown  in  the  figure. 

Six  Phases  are  obtained  from  three  phases  for  use  with 
rotary  converters  by  means  of  transformers  having  two  secondary 


POWER  TRANSMISSION 


windings  or  by  bringing  both  ends  of  each  winding  to  opposite 
points  on  the  rotary-converter  winding,  utilizing  the.  converter 
winding  for  giving  the  six  phases.  The  latter,  shown  in  fig.  27, 
is  known  as  a  diametrical  connection.  When  transformers  with 


1000 

-  1000    -^t-   1000 


'WVA/WW 


VAVvVWWv| 


100  -^-100 
100 


J 


AAA^AAA* 


100 


578 


1000 


1000 


^-1000  -H 

1000J-1000 


+— 1000   -, 
LOOO-^1000* 


V^v/^A/^AA^^~^v^AA^AA^A^^AAAAAA^^A/  WV\MAAA/^-AAA/\AWWV~*~AA/WWWV 

^VWNAAAA/| 


100 


1000 


1000 


.  25. 


two  secondaries  are  used,  the  secondaries  may  be  connected  in  six- 
phase  Y  or  six-phase  A  as  shown  in  Figs.  28  and  29.  When  the 
Y -connection  is  used,  the  common  connection  of  each  set  of  sec- 
ondaries is  made  at  the  opposite  ends  of  the  coils.  This  leaves  the 
free  ends  directly  opposite  or  180°  different  in  phase.  The  way  in 


POWER   TRANSMISSION 


which  these  ends  are  brought  out  to  give  six  phases  is  best  illus- 
trated by  means  of  the  two  triangles  arranged  as  shown  in  Fig.  30, 
which  have  their  points  numbered  corresponding  to  the  connec- 


TEASER 


''  § 


MAIN 


1000 
Fig.  26. 


100 


tion  in  Fig.  28.     In  Fig.  29  one  A  is  reversed  with  respect  to  the 
other,  and  six  phases  are  brought  about  in  this  manner. 

Single  transformers,  constructed  for  three-phase  and  six-phase 
work,  are  now  being  manufactured  in  this  country,  and  they  are 


—  wvwvw 

|>/vWWW 

-^AA/WVM 

~  WWWA/1 

K/WVWV 

K/WWWV/ 

Fig.  27. 


43  65  2 

Fig.  28. 


being  used  to  an  increasing  extent.  They  are  a  little  cheaper  to 
build  for  the  same  total  output,  and  save  floor  space,  but  are  not 
so  flexible  as  three  single-phase  transformers. 

Where  other  conditions  allow,  a  A  to  A-connection  is  prefer- 
able, for  with  this  connection,  if  one  transformer  is  injured,  it 


PO\YER   TRANSMISSION 


may  be  taken  out  of  circuit  and  the  remaining  two  will  maintain 

«'  t~> 

the  service,  and  may  be  loaded  up  to  §  of  the  former  capacity  of 
the  system.  In  the  Y-connection,  however,  the  voltage  impressed 

on   the  transformer  winding   is  only  =   .58   times   the  volt- 

age of  the  line,  thus  making  it  possible  to  construct  a  transformer 
with  a  fewer  number  of  turns.  The  windings  must  be  insulated 
from  the  case,  however,  for  a  potential  equal  to  the  line  potential, 
unless  the  neutral  point  be  grounded  when  the  potential  strain  to 
which  the  transformer  is  liable  to  be  subjected,  under  ordinary 

1 

conditions,  is  reduced  to  ~*~r~  of  its  value  when  the  neutral  is  not 


grounded.  For  small  transformers 
wound  for  high  potential  the  cost  is  in 
favor  of  the  Y  -connection. 


k/wwv 

1 

K/VWVWj 

kW> 

/WW1 

1 

X 

| 

1  634-52 

Fig.  29. 

Choice  of  Frequency.  The  frequencies  in  extended  use  at 
present  in  this  country  are  25,  40,  and  00  cycles,  25  or  <50  cycles 
being  met  with  more  frequently  than  40  cycles.  Formerly,  a  fre- 
quency of  125  or  133  cycles  per  second  was  quite  often  employed 
for  lighting  purposes,  but  these  are  no  longer  considered  standard. 

The  advantages  of  the  higher  frequency  are: 

1.  Less  first  cost  and  smaller  size  of  generators  and  transformers  for 
a  given  output. 

2.  Better  adapted  to  the  operation  of  arc  or  incandescent  lamps. 
Lamps,  when  run  below  40  cycles,  especially  low  candle-power  incandes- 
cent lamps  at  110  volts  or  higher,  are  liable  to  be  trying  to  the  eyes  on 
account  of  the  flicker. 


50  POWER  TRANSMISSION 

Its  disadvantages  are: 

1.  Inductance  and  capacity  effects  are  greater,  hence  a  poorer  regu- 
lation of  the  voltage.     The  charging  current  is  directly  proportional  to  the 
frequency  arid  this  amounts  to  considerable  in  a  long  line. 

2.  There  is  greater  difficulty  in  parallel  operation  of  the  high-fre- 
quency machines  due  to  the  fact  that  the  armature  reactions  of  the  older 
types  of  high-frequency  machines  are  .high. 

3.  Machines  for  high  frequencies  are  not  so  readily  constructed  for 
operation  at  slow  speeds.    This,  however,  will  cease  to  be  an  objection 
with  the  increasing  use  of  the  steam  turbine. 

4.  Not  well  adapted  to  the  operation  of  rotary  converters  and  single- 
phase  series  motors  on  account  of  added  complications  in  construction  and 
increased  commutator  troubles. 

A  frequency  of  BO  cycles  is  usually  adopted  if  the  power  is  to 
be  used  for  lighting  only,  and  25  cycles  are  better  for  railway  work 
alone.  By  the  use  of  frequency  changers  the  frequency  of  any  sys- 
tem may  be  readily  changed  to  suit  the  requirements  of  the  service. 

OVERHEAD   LINES. 

Having  considered  the  calculation  of  the  electrical  constants 
of  a  transmission  line  and  distributing  system,  we  turn  next  to  the 
mechanical  features  of  the  installation  of  the  conductors  and  find 
two  general  methods  of  running  the  wires  or  cables. 

In  the  first  method  the  conductors  are  run  overhead  and  sup- 
ported by  insulators  attached  to  pins  in  cross-arms  which,  in  turn, 
are  fastened  to  the  supporting  poles.  In  the  other  methods  the 
cables  are  placed  underground  and  are  supported  and  protected  by 
some  form  of  conduit. 

Overhead  construction  is  used  when  the  lines  are  run  through 
open  country  or  in  small  towns.  It  forms  a  cheap  method  of  pro- 
viding satisfactory  service  and  is  reliable  when  carefully  installed. 
It  has  the  advantage  that  the  wires  may  be  placed  some  distance 
apart  and,  being  air-insulated,  the  capacity  of  the  line  is  much  less 
than  that  of  underground  conductors. 

The  old  practice  in  overhead  line  construction  has  always  been 
to  consider  the  design  and  erection  of  the  line  as  work  that  anyone 
could  do,  it  being  taken  as  the  simplest  part  of  the  electrical 
system.  As  a  result,  the  line  was  a  source  of  a  great  deal  of  trouble 
which  was  laid  to  almost  any  other  cause  than  poor  construction. 
The  overhead  line,  when  used,  must  be  considered  as  a  part  of  the 


POWER   TRANSMISSION  51 


power  plant  and  it  should  receive  as  careful  attention  as  any  part 
of  the  central  station  or  substation.  It  often  has  to  meet  much 
more  severe  conditions  than  the  power  plant  itself  and  it  is  respon- 
sible to  a  very  large  extent  for  the  reliability  of  service. 

The  new  way  of  treating  the  question  of  overhead  lines  is  to 
consider  them  as  structures  which  must  be  designed  to  meet  cer- 
tain strains  just  as  a  bridge  or  similar  structure  is  designed.  This 
is  especially  true  when  steel  or  iron  poles  are  used  as  is  the  case 
in  nearly  all  transmission  lines  abroad. 

The  design  of  an  overhead  line  may  be  divided  into  five  parts: 

1.    Location  of  line. 

±     Supports  for  the  line,  pole,  and  cross-arms. 

Insulators  and  pins. 

Stresses  sustained  by  the  pole  line. 

Conductors,  material,  size. 

Some  of  these  are  purely  mechanical  features  while  others  are 
both  mechanical  and  electrical.  Let  us  take  them  up  in  the  order 
named. 

Location  of  Line.  The  location  of  the  line  takes  into  account 
the  territory  over  which  the  line  must  be  run  with  respect  to 
contour,  direction,  and  freedom  from  obstructions  as  well  as  pos- 
sible right  of  way.  Width  of  streets,  kind  and  height  of  buildings, 
liability  to  interference  with  or  from  other  systems  must  be  con- 
sidered, when  such  are  present.  The  right  of  way  for  electric  lines 
may  be  secured,  in  some  cases,  along  a  railway  or  public  road  when 
its  location  is  comparatively  simple,  provided  it  is  not  necessary 
to  interfere  with  adjoining  property.  When  adjoining  property 
must  be  interfered  with,  or  when  the  line  is  to  run  over  sections 
containing  no  roads,  it  is  usually  possible  to  form  contracts  with 
the  property  owner  such  as  shall  free  the  line  from  future  inter- 
ference by  the  property  owner.  In  general,  the  cost  of  such  con- 
tracts will  be  comparatively  low.  Again,  the  right  of  way  may 
be  purchased  outright  as  is  preferable  when  right  of  way  is  being 
secured  for  high-speed  electric  railways.  When  the  demands  for 
right  of  way  are  in  excess  of  a  reasonable  amount,  the  process  of 
condemnation  of  property  may  be  resorted  to  or  the  direction  of 
the  line  may  be  changed  so  as  to  avoid  such  locations.  A  prelimi- 
nary survey  of  the  line  should  be  made  at  the  time  the  route  is 


•V* 


POWER   TRANSMISSION 


being  located,  such  a  survey  consisting  of  the  approximate  location 
of  the  poles,  notes  of  the  changes  in  direction  and  level  of  the 
ground  as  well  as  of  its  character.     This  survey  aids  in  the  selec- 
tion of.  material  to  be  delivered  to  the  different  parts  of  the  line. 
Changes  in  level  are  compensated  for   as    much  as    possible    by 
selecting  long  poles  for  the  low  places  and    short  poles  for  the 
higher  elevations,  thus  reducing  the  unbalanced  strains  in  the  line. 
The  heavier  poles  should  be  used   where  there  is  a 
change  in  direction,  where  the  line  is  especially  ex- 
-^Tf!*—         posed  to  the  wind  or  where  branch  lines  are  taken  off. 
It  is  sometimes  necessary  that  power  lines  be  run  on 
the  same  poles  as  telephone  wires,  in  which  case  the 
power  conductors  should,  preferably,  be  located  above 
the  telephone  wires. 

Supports,  Poles.  In  this  country,  the  support 
for  ferial  lines  consists  almost  universally  of  wooden 
poles  to  which  the  cross-arms,  bearing  the  insulator 
pins,  are  attached.  These  poles  may  be  either  natural 
grown  or  sawn.  Abroad,  the  use  of  metal  poles  pre- 
vails. In  order  to  determine  the  proper  cross-section 
of  a  pole  it  may  be  regarded  as  a  beam  fixed  at  one 
end  and  loaded  at  the  other,  this  load  consisting  of  the 
weight  of  the  wire,  with  attendant  snow  or  sleet,  which 
tends  to  produce  compression  in  the  pole,  and  the 
tension  of  the  wires  together  with  the  effect  of  wind 
pressure,  which  tends  to  produce  flexure.  Only  the 
Fig.  31.  latter  stresses  need  be  considered  in  selecting  a  pole 
for  ordinary  transmission  lines.  The  poles  are  in  the 
shape  of  a  truncated  cone  or  pyramid,  the  equation  of  which  is: 


d{  and 
spectively. 


y  ~-  diameter  of  any  section. 

x  ==  distance  from  the  top  of  the  pole. 

I  —  length  of  pole. 

72  =  diameter  of  the  pole  at  the  top  and  bottom  re- 


POWER TRANSMISSION  53 


The  proper  taper  for  a  pole  should  be  such  that  d,  =  J  of  </,. 
If  d.}  >  |  dt  the  pole  is  heavier  than  need  be  as  it  would  tend  to 
break  below  the  ground.  If  less  than  |  <:/,,  the  pole  will  tend 
to  break  above  the  ground  and  the  material  is  not  distributed  to 
the  best  advantage. 

In  calculating  the  size  of  pole  necessary  to  stand  a  certain 
stress,  we  have,  from  the  principles  of  Mechanics, 


M  —  moment  of  resistance. 
I    =  moment  of  inertia. 

S    —  stress  in  the  section   at  </2  at  which  point  the  pole  is 
least  able  to  withstand  the  strain  which  comes  on  it. 

M  =  P/  where  P  is  the  tension  in  the  wires  and  /  =  length 

o 

of  pole  in  inches. 

For  a  round  pole,  I  =  - 

()4r 

S1JY/8. 


and  we  have 


32 

Solving  for  8,  S  —    ^  /3 

For  a  sawn  pole  with  square  cross-sections  the  value  of  I  is: 


Sd\  6  PI 

and  PI  •=  -^  or  b  =    —^~ 

The  value  for  S  should  not  exceed  a  certain  proportion  of  the 
ultimate  strength  of  the  material.     If  T  represents  the  ultimate 

T 

strength  in  pounds  per  square  inch,  then  P  =  —  where  n  is  known 

as  the  factor  of  safety  and  is  ordinarily  not  taken  less  than   10  for 
wooden  structures.     A  high  factor  of  safety  is  necessary  on  account 


54  POWER  TRANSMISSION 


of   the  material  not  being  uniform,  and  the    uncertainty  of    the 
value  of  T. 

Following  are  commonly  accepted  values  of  T: 

Yellow  pine: 5,000  -  12,000  pounds 

Chestnut 7,000-18,000       '< 

Cedar 11,500 

Redwood 11,000 

T 

The  value  of  —  should  not  be  over  about  800  for  natural  poles 
u> 

and  GOO  for  sawn  poles. 

d.,  is  measured  at  the  ground  line  of  the  pole,  not  at  the  base. 

Consider  a  pole  of  circular  cross-section  having  a  length  of 
35  feet  and  a  diameter  at  the  ground  line  of  12  inches.  Using 

T 

-  000,  what  is  the  maximum  allowable  stress  that  should  be 

u 

applied  at  the  end  of  the  pole  ? 
327V 

7Td\ 

P  =  600 

I  =  =35  >[  12  ^  420  inches. 
d2  =  12 

32  X  000  X  420 
S  -    3.1410  X  1728    =  i'480  lbs- 

It  is  customary  to  select  a  general  type  of  pole  for  the  whole 
line  determined  from  calculations  based  on  the  above  formulae, 
after  the  tension  in  the  wire  has  been  found,  and  not  to  apply 
such  calculations  to  every  section  of  the  line.  The  line  is  then 
reinforced,  where  necessary,  by  means  of  guy  wires  or  struts. 

Following  are  some  of  the  general  requirements  for  poles: 

Spacing  should  not  exceed  40  to  45  yards. 

Poles  should  be  set  at  least  five  feet  in  the  ground  with  an  addi- 
tional six  inches  for  every  five  feet  increase  in  length  over  thirty-five  feet. 
Special  care  in  setting  is  necessary  when,  the  ground  is  soft.  End  and 
corner  poles  should  be  braced  and  at  least  every  tenth  pole  along  the  line 
should  be  guyed  with  %  or  %-inch  stranded  galvanized  iron  wire. 

Regular  inspection  of  poles,  at  least  yearly,  should  be  main- 
tained and  defective  poles  replaced.  The  condition  of  poles  is  best 
determined  by  examination  at  the  base. 


POWER  TRANSMISSION  55 

Poles  should  preferably  be  of  good,  sound  chestnut,  cedar,  or 
redwood.  Other  kinds  of  wood  are  sometimes  used,  the  material 
depending  largely  on  the  section  of  the  country  in  which  the  line 
is  to  be  erected  and  the  timber  available.  Natural  poles  should  be 
shaved,  roofed,  gained,  and  given  one  coat  of  paint  before  erecting. 

Special  methods  of  preserving  poles  have  been  introduced, 
chief  among  which  may  be  considered  the  process  of  creosoting. 
Creosoting  consists  of  treating  the  poles  with  live  steam  at  a  tem- 
perature of  225  to  250°,  so  as  to  thoroughly  heat  the  timber,  after 
which  a  vacuum  is  formed  and  then  the  containing  cylinder  is 
pumped  full  of  the  preserving  material,  a  pressure  of  about  100 
pounds  per  square  inch  being  used  to  force  the  desired  amount  of 
material  into  the  wood.  The  butts  of  poles  are  often  treated  with 
pitch  or  tar,  but  this  should  only  be  applied  after  the  pole  is 
thoroughly  dry. 

Guying  of  pole  lines  is  one  of  the  most  important  features  of 
construction.  Guys  consist  of  three  or  more  strands  of  wTire, 
twisted  together,  fastened  at  or  near  the  top  of  the  pole,  and  car- 
ried to  the  ground  in  a  direction  opposite  to  that  of  the  resulting 
strain  on  the  pole  line.  The  lower  end  is  attached  to  some  form 
of  guy  stub  or  guy  anchor.  This  may  be  a  tree,  a  neighboring 
pole,  a  short  length  of  pole  set  in  the  ground,  or  a  patent  guy 
anchor.  Guy  stubs  are  set  in  the  ground  at  an  inclination  such 
that  the  guy  makes  an  angle  of  90°  with  the  stub  or  with  the  axis 
of  the  stub  in  the  direction  of  guy,  the  stub  in  the  latter  case  being 
held  in  place  by  timber  or  plate  fastened  at  right  angles  to  the 
bottom  of  the  stub.  Such  a  timber  is  known  as  a  "  dead  man  ". 

The  angle  the  guy  wire  makes  with  the  pole  should  be  at  least 
20°.  When  there  is  not  room  to  carry  the  guy  far  enough  away 
from  the  base  of  the  pole  to  bring  this  angle  to  20°  or  more,  a 
strut  may  be  used.  This  consists  of  a  pole  slightly  shorter  and 
lighter  than  the  one  to  be  reinforced.  It  is  framed  into  the  line 
pole  near  the  top  and  set  in  the  ground  at  a  short  distance  from 
the  base  of  the  pole  on  the  opposite  side  of  the  pole  from  that  on 
which  a  guy  would  be  fastened. 

Stranded  galvanized  steel  guy  wire  is  used  for  guys.  There 
are  two  general  methods  of  attaching  the  guys  to  the  top  of  the 
pole.  In  the  one,  a  single  guy  is  run,  attached  at  or  near  the 


56 


POWER  TRANSMISSION 


middle  cross-arm,  while  in  the  other,  known  as  "  Y"  guying,  two 
wires  are  run  to  the  top  of  the  pole,  one  at  the  upper  the  other  at 
the  lower  arm,  and  these  united  into  a  single  line  a  short  distance 
from  the  pole. 

Head  guying,  guying-in  the  direction  of  the  line,  is  used  when 
the  line  is  changing  level  and  for  end  poles.    The  guys  are  attached 


Fig.  3i>. 

near  the  top  of  one  pole  and  run  to  the  bottom  of  the  pole  just 
above.  Fig.  32  shows  several  methods  of  reinforcing  pole  lines. 
Special  methods  are  adapted  as  necessary. 

Cross-Arms.  The  best  cross-arms  are  made  of  southern  yellow 
pine.  Oak  is  also  used  to  a  large  extent.  They  should -be  of 
selected  well-seasoned  stock.  The  iisual  method  of  treatment  is  to 
paint  them  with  white  lead  and  oil.  The  size  of  cross-arms  and 
spacing  of  pins  have  not  been  thoroughly  standardized.  For  cir- 


POWER  TRANSMISSION 


57 


cuits  up  to  5,000  volts,  3^  X  ±^  or  3|  X  4J;"  cross-arms  with 
spacing  between  pins  of  16  inches,  the  pole  pins  being  spaced  22 
inches,  are  recommended.  For  higher  voltages,  special  cross-arms 
and  spaciijgs  are  necessary.  The  cross-arms  should  be  spaced  at 
least  2-4  inches  between  centers,  the  top  arm  being  placed  12  inches 
below  the  top  of  the  pole.  They 
are  usually  attached  to  the  pole  by 
means  of  two  bolts  and  are  braced 
by  galvanized  iron  braces  not  less 
than  11  X  f\  inch  and  about  2<S 

inches  long-. 

r? 

Cross-arms  are  placed  on  al- 
ternate sides  of  the  poles  so  as  to 
prevent  several  of  them  from  being 
pulled  off  should  one  become 
broken  or  detached.  On  corners 
or  curves  double  arms  are  use'd 
In  European  practice,  the  cross-arm 
is  done  away  with  to  a  large  extent, 

the  wire  beino1  mounted  on  inSUla- 
^D 

tors  attached  to  iron  brackets 
mounted  one  above  the  other.  Fig. 
33  gives-  an  idea  of  this  con- 
struction. 

Insulators.  Electrical  leak- 
age between  wires  must  be  pre- 
vented in  some  way  and  various 
forms  of  insulators  are  depended 
upon  for  this  purpose.  The  ma- 
terial used  in  the  construction  of 
these  insulators  should  possess  the 
following  properties:  high  specific 
resistance;  surface  not  readily  de- 
stroyed and  one  on  which  moisture 


Fig.  33. 


does  not  readily  collect;  mechanical  strength  to  resist  both  strain 
and  vibrating  shocks.  Its  design  must  be  such  that  the  wire  can 
be  readily  fastened  to  it  and  the  tension  of  the  wire  will  be  trans- 
mitted to  the  pin  without  producing  a  strong  strain  in  the  insu- 


58 


POWER  TRANSMISSION 


HEIGHT  3|"TESTED  AT  50,000V  HEIGHT    3"  TESTED  AT  30,000V. 


HEIGHT   4^  TESTED  AT  70,000V.  HEIGHT    7\  TESTED  AT  80,000V. 


HEIGHT    4|  TESTED  AT  5QOOOV.  HEIGHT    4$  TESTED  AT  50,000V. 


Ti r  _, w 

HEIGHT   3i  TESTED  AT  40,000V.  HEIGHT  4^    TESTED  AT  40,000 V. 

Fig.  34. 


POWER  TRANSMISSION 


f  Diet. 

Cut  Eccentric  in 
Bolt  Cutter 


Composite  Pin 

for 
Hiqh  Tension  Insulator 


lator.  Leakage  surface  must  be  ample  for  the  voltage  of  the  line 
and  so  constructed  that  a  large  portion  of  it  will  be  protected  from 
moisture  during  rainstorms.  The  principal  materials  used  are 
glass  and  porcelain. 

Porcelain  has  the  advantage  over  glass  that  it  is  less  brittle 
and  generally  stronger  and  that  it  is  less  hygroscopic,  that  is,  mois- 
ture does  not  so  readily  collect  on  and  adhere  to  its  surface.  Glass 
is  less  conspicuous  and  is 
cheaper  for  the  smaller  in- 
sulators. Both  materials 
are  freely  used  for  the  con- 
struction of  high-tension 
lines,  while  the  use  of  glass 
prevails  for  the  low-tension 
circuits. 

All  line  insulators  are 
of  the  petticoat  type  and 
are  made  up  in  various 
shapes  and  sizes.  The 
larger  size  porcelain  insu- 
lators are  made  up  in  two 
or  more  pieces  which  are 
fastened  together  by  means 
of  a  paste  formed  of  lith- 
arge and  glycerine.  The 
advantages  of  this  form  of 
construction  are  greater 
uniformity  of  structure, 
and  each  part  may  be  tested  separately.  1<  "ig.  34  shows  several 
forms  of  insulators  now  in  use  with  the  voltage  at  which  they 
are  tested.  The  test  applied  to  an  insulator  for  high-tension  lines 
should  be  at  least  double  the  voltage  of  the  line,  and  some  engineers 
recommend  three  times  the  normal  voltage. 

Pins.  Pins  made  of  locust  wood  boiled  in  linseed  oil  are  pre- 
ferred for  voltages  up  to  5,000.  Above  this  special  pins  are  used. 
Wood  pins  are  often  objected  to  on  account  of  the  burning  or 
charring  which  takes  place  in  certain  localities,  and  iron  pins  are 
being  used  to  a  large  extent.  Fig.  35  shows  the  dimensions  of  such 


60  POWER   TRANSMISSION 


a  pin  used  on  a  (30,  000-  volt  line.  The  insulator  is  fastened  to  the 
pin  by  means  of  a  thread  in  a  lead  lug  which  is  cast  on  top  of  the 
pin.  The  insulators  in  the  construction  shown  in  Fig.  33  are 
cemented  to.  the  iron  brackets. 

The  Stresses  sustained  by  the  line  may  be  classified  as 
follows  : 

1.  Weight  of  wire,  which  includes  insulation,  and  snow  and  sleet 
which  may  be  supported  by  the  wire.* 

2.  Wind  pressure  upon  the  parts  of  the  line. 

The  strain  produced  by  the  weight  of  the  \vire  on  the  pole 
itself  need  not  be  considered  except  in  exceptional  cases,  because 
if  the  pole  is  sufficiently  strong  to  withstand  the  bending  strains, 
it  is  more  than  strong  enough  to  withstand  the  compression  due 
to  the  weight  of  the  wires. 

^ 

8.    Tension  in  the  wire  itself. 

Langley  shows  the  pressure  of  the  wind  normal  to  Hat  sur- 
faces to  be  equal  to: 

,  =  .0030  *  =  -. 


j>  =  pressure  in  pounds  per  sq.  ft. 
v  --  velocity  in  miles  per  hour. 

For  cylindrical  surfaces  the  amount  of  pressure  is  §  that  ex- 
erted on  a  flat  surface  of  a  width  equal  to  the  diameter  of  the 
cylinder.  Without  great  error  we  may  assume  that*  the  maximum 
wind  pressure,  and  that  for  which  calculation  is  necessary,  is  that 
at  right-angles  to  the  line,  and  a  value  of  thirty  pounds  per  square 
foot  is  sufficient  allowance  for  exposed  places,  while  twenty  pounds 
]>er  square  foot  is  considered  sufficient  where  the  line  is  par- 
tially sheltered. 

Example.  What  is  the  pressure,  due  to  the  wind,  on  the 
wires  of  a  pole  line  containing  three  number  0000  wires,  the  poles 
being  spaced  45  yards  and  the  velocity  of  the  wind  such  that  the 
pressure  may  be  taken  as  30  pounds  per  square  foot. 

The  diameter  of  a  number  0000  wire  is  .400  inch.  The  area 
against  which  the  wind  exerts  its  force  may  be  considered  as: 

'2        3  X  45  X  3  X  1'2  X  .400 
-77-)  ~iTT~  ~  °-l()<)  square  feet. 


POWER   TRANSMISSION  61 


5.100  )(  30  =  155  pounds  pressure  due  to  wind  on  wires. 

The  most  important  strain-producing  factor  in  a  line  is  that 
due  to  the  tension  in  the  wire  itself.  A  wire  suspended  so  as  to 
hang  freely  between  two  supports  assumes  the  form  of  curve  known 
as  a  catenary,  but  for  ordinary  work  the  curve  may  be  taken  as  a 
parabola  the  equation  of  which  is  simple  and  from  which  the  fol- 
lowing equations  are  derived  : 

"=i 

~8D~ 

L  =  n  +  S 

When  I)  —  deflection  or  sag  at  lowrest  point  in  feet. 

L   :=  actual  length  of  wire  between  supports  in  feet. 

II  :  =  distance  between  supports  in  feet. 

W  —  weight  of  wire  in  pounds  per  foot. 

Pc  —  horizontal  tension  in  the  wire  at  the  middle  point. 

T 

Pc  =  -  where  T  =  tensile   strength   of   the  wire  and  n  - 

factor  of  safety,  n  =  2  to  0  under  the  conditions  existing  when 
the  wire  is  erected.  The  temperature  changes  in  the  wire  affect 
the"  value  of  this  factor,  it  being  greatest  when  the  temperature  is 
a  maximum,  and  a  minimum  when  the  temperature  is  lowest,  and 
calculation  should  be  for  the  maximum  strain  that  may  come  on 
the  wires. 

If  Lt  =  length  of  a  wire  at  a  given  temperature,  t"  (1. 
and       L^  ==  length  of  a  wire  at  a  given  temperature,  20 J  C. 
Then,    Lt  ;=  L,0  [1  +  k  (t  -  20)]. 

k  ==   .000012  for  iron. 

.0000108  to  .0000114  for  aluminum. 
.0000172  for  copper. 

The  following  table  gives  the  deflection  of  spans  of  wire  in 
inches  for  different  temperatures  and  different  distances  between 
poles,  a  maximum  stress  of  30,000  pounds  per  square  inch  being 
allowed  at  -  10°  F,  which  gives  a  factor  of  safety  of  2  for  hard- 
drawn  copper  wire. 


62 


POWER  TRANSMISSION 


TABLE  VII. 
Temperature  Effects  in  Spans. 


Spans 

in 
Feet. 


TEMPERATURE  IN  DKGKKKS   KAHKKNHK1T. 


-10         30 ''          40     -      o() 


60 


70" 


80  •'         90° 


Deflection  in.  Im-hes. 


50 

.5 

6 

8 

9 

9 

10 

11 

11 

12 

60 

.7 

8 

10 

11 

11 

12 

13 

13 

14 

70 

1. 

10 

11 

12 

13 

14 

15 

15 

17 

80 

1.2 

11 

13 

14 

15 

16 

17 

18 

19 

90 

1.6 

13 

14 

16 

17 

18 

19 

20 

21 

100 

1.9 

14 

16 

17 

19 

20 

21 

23 

24 

no 

2.3 

16 

18 

19 

21 

22 

24 

25 

26 

120 

2.8 

17 

19 

21 

22 

24 

26 

27 

28 

140 

3.7 

20 

23 

25 

27 

28 

30 

32 

.33 

160 

4.9 

23 

26 

28 

30 

32 

34 

36 

38 

180 

6.2 

26 

29 

32 

34 

37 

39 

41 

43 

200 

7.7 

31 

33 

36 

38 

41 

43 

45 

48 

The  above  formulae  apply  directly  to  lines  in  which  the  poles 
are  the  same  distance  apart  and  on  the  same  level,  and  any  number 
of  spans  may  be  adjusted  at  one  time  by  applying  the  calculated 
stress  at  the  end  of  the  wire  and  the  line  will  be  in  equilibrium; 
that  is,  there  will  be  no  strain  on  the  poles  in  the  direction  of  the 
wires.  Special  care  must  be  taken  to  preserve  this  equilibrium  when 
the  length  of  span  changes  or  when  the  level  of  the  pole  tops  varies, 
and  this  is  accomplished  by  keeping  Pc  and  ti  constant  for  every. span. 

What  is  the  tension  in  pounds  per  square  inch  at.  the  center 
of  a  span  of  number  0000  wire  when  the  poles  are  120  feet  apart 
and  the  sa  is  16  inches  ? 


^TT 

II      :     =    120 
I)     : 


"W  =  .(>4  pounds. 

(120)2  X  .64 


P,  = 


8  X 


=  864  pounds 


The  cross-section  of  number  0000  wire  is,— 
77"  X   (.23)2  ==  .1662  square  inches. 
864  -T-  .1662  ==  5200  pounds  per  square  iach. 


POWER  TRANSMISSION 


The  regulation  of  the  system  and  the  amount  of  power  lost  in 
transmission  together  determine  the  cross-section  of  the  conductors 
to  be  used.  The  amount  of  power  lost,  for  most  economical  opera- 
tion can  be  determined  from  the  cost  of  generating  power  and  the 
fixed  charges  on  the  line  investment.  Either  copper  or  aluminum 
wire  or  cables  may  be  used.  The  latter  is  lighter  in  weight  but 
more  care  must  be  taken  in  erecting  and  it  is  more  difficult  to 
make  joints. 

UNDERGROUND  CONSTRUCTION. 

In  large  cities  or  other  localities  where,  if  overhead  construc- 
tion be  used,  the  number  of  conductors  becomes  so  great  as  to  be 
objectionable,  not  alone  on  account  of  appearance  but  also  on 
account  of  complication  and  danger,  the  lines  are  run  underground. 
The  expense  of  installing  underground  systems  is  very  great  com- 
pared with  that  of  overhead  construction,  but  the  cost  of  mainten- 
ance is  much  less  and  the  liability  to  interruption  of  service,  due 
to  line  troubles,  greatly  reduced.  The  essential  elements  of  an 
underground  system  are  the  conductor,  the  insulator,  and  the  pro- 
tection. The  conductor  is  invariably  of  copper,  the  insulator  may 
be  rubber,  paper,  some  insulating  compound,  or  individual  insu- 
lators, depending  on  the  system,  while  the  protection  takes  one  of 
several  forms.  The  system,  as  a  whole,  may  be  divided  into 

,  Bolid  or  built-in  systems. 

Trench  systems. 
Drawing-iii  systems. 

As  an  example  of  the  first,  we  have  the  Eflixon,  Tnbe  xyxttin* 
which  is  especially  adapted  to  house-to-house  distribution  and  is 
used  to  a  large  extent  for  direct-current  three-wire  distribution  in 
congested  districts.  It  is  made  up  of  copper  rods  as  conductors 
(three  of  equal  size  for  mains  and  the  neutral  but  \  the  size  of  the 
main  conductors  in  feeders),  which  are  insulated  from  each  other 
by  an  asphaltum  compound.  This  compound  also  serves  as  an 
insulation  from  the  protecting  case,  which  consists  of  wrought- 
iron  pipe.  Pilot  wires  are  also  often  installed  in  the  feeder  tubes. 
This  tube  is  built  up  in  sections  about  twenty  feet  long.  In  insu- 
lating the  conductors,  they  are  first,  loosely  wrapped  with  jute 
rope  so  as  to  keep  them  from  making  contact  with  each  other, 


POWER  TRANSMISSION 


Fig.  36. 


POWER  TRANSMISSION  r,r, 

and  with  the  pipes,  and  the  heated  asphaltum  forced  into  the  tube 
from  the  bottom,  when  the  tube  is  in  a  vertical  position.  Tlie 
ends  of  the  conductors  and  the  tubes  must  be  joined  and  properly 
insulated  in  a  completed  system.  Special  connectors  are  furnished 
for  the  conductors,  and  cast-iron  coupling  boxes  are  fitted  to  the 
ends'  of  the  tube  as  shown  in  Fig.  30.  After  the  conductors  are 
properly  connected,  the  cap  is  put  on  this  coupling  box  and  the 
inside  space  then  filled  with  insulating  compound  through  a  hole 
in  the  cap.  This  hole  is  later  fitted  with  a  plug  to  render  the  box 
air-tight.  The  system  is  a  cheap  one,  though  the  joints  are  expen- 
sive. It  is  not  adapted  to  high  potentials. 

The  Siemens-IIdlske  system  of  iron -taped  cables  consists  of 
insulated  cables  encased  in  lead  to  keep  out  moisture,  this  lead 
sheathing  being  in  turn  wrapped  with  jute  which  forms  a  bedding 
for  the  iron  tape.  The  iron  tape  is  further  protected  by  a  wrap- 
ping thoroughly  saturated  with  asphaltum  compound.  These 
cables  may  be  made  up  in  lengths  of  from  500  to  000  feet. 

In  unexposed  places,  such  as  across  private  lands,  the  steel 
taping  may  be  omitted  and  the  lead  sheathing  simply  protected  by 
a  braid  or  wrapping  saturated  with  asphaltum. 

The  Trench  system  consists  of  bare  or  insulated  conductors 
supported  on  special  forms  of  insulators  as  in  overhead  construc- 
tion, the  whole  being  installed  in  small  closed  trenches.  As  this 
system  is  not  used  to  any  extent  in  America,  but  one  system,  the 
Crompton  system,  will  be  described. 

In  the  Crompton  system,  bare  copper  strips  are  used,  each  1 
to  li  inches  wide  and  |  to  ^  inch  thick.  These  strips  rest  in 
notches  on  the  top  of  porcelain  or  glass  insulators,  supported  by 
oak  timbers  embedded  in  the  sides  of  the  cement-lined  trench. 
This  trench  is  covered  with  a  layer  of  flagstone.  These  insulators 
are  spaced  about  50  feet  and  about  every  800  feet  a  straining 
device  is  installed  for  takinor  up  the  sag  in  the  conductors.  Hand- 

01  O 

holes  are  located  over  each  insulator. 

There  are  several  of  the  drawing -in  systems,  and  certain  of 
these  have  come  to  be  considered  standard  underground  construc- 
tion in  the  United  States.  It  is  no  longer  deemed  advisable  to 
construct  ducts  which  will  serve  as  insulators,  but  they  are  de- 


POWER   TRANSMISSION 


pended  on  for  mechanical   protection   only,  and   should  fulfill   the 
following  requirements: 

They  must  have  a  smooth  interior,  free  from  projections,  so  that  the 
cables  may  be  readily  drawn  in  and  out. 

They  must  be  reasonably  water-tight. 

They  must  be  strong  enough  to  resist  injury  due  to  street  traffic  and 
accidental  interference  from  workmen. 

Among  the  materials  used  for  duct  construction  may  be  men- 
tioned: iron  or  steel,  wood,  cement,  and  terra  cotta.  Wood  is 
used  in  the  form  of  a  trough  or  box,  or  in  the  form  of  wooden 

TO    STREET    SURFACE 

A  MINIMUM-OF  3' 
PLANKS 


"-KVI 


-2'APPROX- 
Fig.  37. 

pipes.  The  latter  is  known  as  "pump  log"  conduit.  The  wood 
used  for  this  purpose  must  be  very  carefully  seasoned  and  then 
treated  with  some  antiseptic  compound,  such  as  creosote,  in  order 
for  the  duct  to  give  satisfactory  service.  If  improperly  treated, 
acetic  acid  is  formed  during  the  decay  of  the  wood,  and  this  attacks 
the  lead  covering  of  the  cable,  destroying  it  and  allowing  moisture 
to  deteriorate  the  insulation.  Wood  offers  very  little  resistance  to 
the  drawing  in  of  the  cables,  and  it  is  a  cheap  form  of  conduit, 
though  it  cannot  be  depended  on  for  long  life. 

One  of  the  best  and  at  the  same  time  most  expensive  systems 
is  the  one  using  wrought-iron  pipes,  laid  in  a  bed  of  concrete. 
The  ordinary  construction  of  the  duct  consists  of  digging  a  trench 


POWER  TRANSMISSION  07 


of  the  desired  size  and  covering  the  bottom,  after  it  is  carefully 
graded,  with  a  layer  of  good  concrete  from  two  to  four  inches  thick. 
Such  a  cement  may  consist  of  Rosendale  cement,  sand,  and  broken 
stone  in  the  ratio  of  2,  3,  5,  the  broken  stone  to  pass  through  a 
sieve  of  H-inch  mesh.  The  sides  of  the  trench  are  lined  with  1A- 
inch  planks.  The  first  layer  of  pipes  consisting  of  wrought-iron 
pipes  3  to  4  inches  in  diameter,  20  feet  long,  and  £  inch  thick, 
joined  by  means  of  water-tight  .couplings,  is  laid  on  this  concrete, 
and  the  space  around  and  above  them  filled  with  concrete.  A  sec- 
ond layer  of  pipes  is  laid  over  this,  and  so  on.  A  covering  of  con- 
crete 2  to  3  inches  thick  is  placed  over  the  last  layer,  and  a  layer 
of  2-inch  plank  is  placed  over  all,  to  protect  against  injury  by 
workmen.  Fig.  37  shows  a  cross-section  of  such  duct  construc- 
tion. The  pipe  should  be  reamed  so  as  to  remove  any  internal 
burs  which  might  injure  the  insulation  during  the  process  of 
drawing  in. 

A  modification  of  this  system  consists  of  the  use  of  cenient- 
liiH'd  wroucjht-irou  pipes.  This  usually  consists  of  eight-foot 
lengths  made  of  riveted  sheet-iron,  pipes.  Rosendale  cement  is 
used  for  the  lining,  this  lining  being -about  |  inch  thick.  .The 
external  diameter  of  the  pipe  is  about  4|  inches.  The  outside  of 
the  pipe  is  coated  with  tar  to  prevent  rusting.  The  sections  have 
a  very  smooth  interior  and  are  light  enough  to  be  easily  handled. 
They  are  embedded  in  concrete,  similar  to  the  system  previously 
described.  Connections  between  the  sections  are  made  by  means 
of  joints,  constructed  on  the  ball-and-socket  principle,  moulded  in 
the  cement  at  the  ends  of  the  sections.  This  forms  a  cheaper  con- 
struction than  the  use  of  full -weight  pipe. 

Earthenware  Conduits.  This  form  of  conduit  is  being  ex- 
tensively used  for  underground  cables.  The  sections  may  be  of 
the  single-duct  or  multiple-duct  type.  The  former  consists  of  an 
earthenware  pipe  from  18  to  24  inches  in  length.  The  internal 
diameter  is  from  2^  to  3  inches.  These  are  laid  on  a  bed  of  con- 
crete, the  separate  tiles  being  laid  up  in  concrete  in  such  a  manner 
as  to  break  joints  between  the  various  ducts.  In  .the  multiple- 
duct  system  the  joints  are  wrapped  with  burlap  and  the  whole 
embedded  in  concrete.  This  form  of  conduit  has  a  smooth  inte- 
rior and  the  cables  are  readily  drawrn  in  and  out.  The  single-duct 


68 


POWER  TRANSMISSION 


type  lends  itself  admirably  to  slight  changes  of  direction  that 
may  be  necessary.  Fig.  38  shows  both  forms  of  duct,  while  Fig. 
39  shows  a  cement-lined  iron -pipe  duct  system,  laid  in  concrete, 
in  course  of  construction. 

Other  forms  of  conduits  are  ducts  formed  in  concrete,  earthen- 
ware troughs,  cast-iron  troughs,  and  libre  tubes. 

Manholes.  For  all  drawing-in  systems,  it  is  necessary  to 
provide  some  means  of  making  connections  between  the  several 
lengths  of  cable  after  they  are  drawn  in,  as  well  as  for  attaching 
feeders.  Since  the  cables  cannot  be  handled  in  lengths  greater 


Fig.  38. 

than  about  500  feet,  and  less  than  this  in  many  cases,  vaults  or 
junction  boxes  must  be  placed  at  frequent  intervals.  Such  vaults 
are  known  as  splicing  vaults  or  manholes.  The  size  of  the  man- 
hole depends  upon  the  number  of  ducts  in  the  system,  as  well  as 
on  the  depth  of  the  conduit.  If  the  ducts  be  laid  but  a  short  dis- 
tance from  the  surface  of  the  street  and  traffic  is  light,  the  cables 
may  be  readily  spliced  with  a  manhole  but  4  feet  square  and  4 
feet  deep.  The  smaller  vaults  are  often  called  "  hand-holes ". 
Deeper  vaults  are  from  5  to  6  feet  square,  and  the  floor  should  be 
at  least  18  inches  below  the  lowest  ducts  on  account  of  convenience 
to  the  workmen  and  to  serve  as  collecting  basins  for  water  which 
gets  into  the  system.  The  ducts  should  always  be  laid  with  a 
gentle  slope  toward  such  manholes. 


POWER  TRANSMISSION  09 


Common  construction  consists  of  a  brick  wall  laid  upon  a  con- 
crete floor,  the  brick  being  laid  in  cement  and  being  coated  inter- 
nally with  cement.  The  cables  follow  the  sides  of  the  manhole 
and  they  are  supported  on  hooks  set  in  the  brickwork.  This 
causes  quite  a  waste  of  cable  in  large  manholes.  Care  should  be 
taken  that  workmen  (Jo  not  use  the  cables,  so  supported,  as  ladders 


Fig.  39. 

in  entering  and  leaving  the  manhole,  as  the  lead  sheathing  maybe 
readily  injured  when  the  cables  are  so  used. 

Conductors  are  drawn  into  place  by  the  aid  of  some  form  of 
windlass.  Special  jointed  rods,  3  to  4  feet  long,  may  be  used  for 
making  the  first  connection  between  manholes  or  a  steel  wire  or 
tape  may  be  pushed  through.  A  rope  is  drawn  into  the  duct  and 
the  cable  is  attached  to  this  rope.  Fig.  40  shows  one  way  in  which 
the  cable  may  be  attached  to  the  rope.  Care  must  be  taken  to  see 
that  no  sharp  bends  are  made  in  the  cable  during  this  process. 
Cable  should  not  be  drawn  in  during  extremely  cold  weather  un- 
less some  means  are  employed  for  keeping  it  warm,  owing  to  the 
liability  of  the  insulation  to  be  injured  by  cracking. 


70 


POWER  TRANSMISSION 


Conduit  systems  must  be  ventilated  in  order  to  prevent  ex- 
plosion due  to  the  collecting  of  explosive  mixtures  of  gas.  Many 
special  ventilating  schemes'  have  been  tried,  but  the  majority  of 
systems  depend  for  their  ventilation  on  holes  in  the  manhole  cov- 
ers. This  prevents  excessive  amounts  of  gas  from  collecting  but 
does  not  always  free  the  system  from  gas  so  completely  as  to  make 
it  safe  for  workmen  to  enter  the  splicing  vault  until  the  impure 
air  has  been  pumped  out. 

The  above  applies  to  the  main  conduit  system.  Auxiliary 
ducts  are  laid  over  the  main  ducts  and  distribution  accomplished 
from  hand -holes  in  this  system. 

It  is  customary  to  ground  the  lead  sheaths  of  the  cables  at 
frequent  intervals,  thus  in  no  way  depending  on  the  ducts  even 
when  made  of  insulating  material,  for  insulation. 


IRON  WIRE 


ROPE 


SHACKLE: 

Fig.  40. 


YARN  SERVING 


Cables.  Well  insulated  copper  cables  are  used  for  under- 
ground systems.  On  account  of  the  fact  that  various  materials, 
such  as  acids  and  oils  which  are  injurious  to  the  insulation,  come 
in  contact  with  the  cable,  it  is  necessary  that  it  be  protected  in 
some  manner.  A  lead  sheath  is  employed  for  this  purpose.  This 
sheath  is  made  continuous  for  the  whole  length  of  the  conductor, 
and  with  its  use  it  is  possible  to  employ  insulating  materials  such 
as  paper  which,  on  account  of  being  readily  saturated  by  moisture, 
could  not  be  used  at  all  without  such  a  hermetically  sealed  sheath. 
Lead  containing  a  small  percentage  of  tin  is  usually  employed  for 
this  purpose.  The  sheath  may  consist  of  a  lead  pipe  into  which 
the  cable  is  drawn,  after  which  the  whole  is  drawn  through  suitable 
dies,  bringing  the  lead  in  close  contact  with  the  insulation  or  the 
casing  may  be  formed  by  means  of  a  hydraulic  press. 

Yarns  thoroughly  dried  and  then  saturated  with  such  materials 
as  paraffin,  asphaltum,  rosin,  etc.,  paper,  both  dry  and  saturated, 


POWER  TRANSMISSION 


71 


anil  rubber  are  the  materials  more  generally  employed  for  insula- 
tion. When  paper  is  employed,  it  is  wound  on  in  strips,  the  cable 
being  passed  through  a  die  after  each  layer  is  applied,  after  which 
it  is  dried  at  a  temperature  of  200°  F  to  expel  moisture.  After 
being  immersed  in  a  bath  of  the  saturating  compound  it  is  taken 
to  the  hydraulic  presses  where  the  lead  sheath  is  put  on. 

When  rubber  insulation  is  used,  the  conductors  are  tinned  to 
prevent  the  action  of  any  uncqmbined  sulphur  which  may  be 
present  in  the  vulcanized  rubber.  The  Hooper  process  consists  of 

usincr  a  layer  of  pure  rubber  next  to  the  conductors  and  usim**  the 

o  J  i  r> 

vulcanized  rubber  outside  of  this.  One  or  two  layers  of  pure  rub- 
ber tape  are  put  on  spirally, 
the  spiral  being  reversed  for 
each  layer.  Rubber  com- 
pound in  two  or  more  layers 
is  applied  over  this  in  the 
form  of  two  strips  which  pass 
between  rollers  which  fold 
these  strips  around  the  core 
and  press  the  edges  together. 


INSULATION 


INSULATION 


(. STRANDED  CONDUCTOR 

Fig.  41. 


Prepared  rubber  tape  is  ap- 
plied over  this,  after  which 
the  insulator  is  vulcanized 
and  the  cable  tested.  If  sat- 
isfactory the  external  protection  is  applied. 

Cable  for  polyphase  work  is  made  up  of  three  conductors  in 
one  sheath.  Fig.  41  shows  a  cross-section  of  cable  manufactured 
for  three-phase  transmission  at  6,600  volts.  The  conductors  of 
this  cable  have  a  cross-section  equivalent  to  a  number  0000  wire, 
to  which  an  insulation  of  rubber  --^-inch  thick  is  applied.  These 
three  conductors  are  twisted  together  with  a  lay  of  about  20 
inches.  Jute  is  used  as  a  tiller,  and  a  second  layer  of  rubber  insu- 
lation gV-inch  thick  is  then  applied.  The  lead  sheath  employed  is 
J-inch  thick,  and  is  alloyed  with  3%  of  tin. 

Joints  in  cables  must  be  carefully  made.  Well- trained  men 
only  should  be  employed.  The  insulation  applied  to  the  joint 
should  be  equivalent  to  the  insulation  of  the  cable  at  other  points, 
and  the  joint  as  a  whole  must  be  protected  by  a  lead  sheath  made 


72 


POWER   TRANSMISSION 


continuous  with  the  main  covering  by  means  of  plumbers'  joints. 

Some  engineers  prefer  rubber,  some  paper  insulation,  but 
both  types  are  giving  good  service,  and  are  used  up  to  voltages  of 
22,000.  It  is  customary  to  subject  each  cable  to  twice  its  normal 
potential  soon  after  it  is  installed.  This  voltage  should  not  be 
applied  or  removed  too  suddenly  as  unnecessary  strains  might  be 
produced  in  this  manner. 

Rubber-insulated  cables  should  never  be  allowed  to  reach  a 
temperature  exceeding  65°  to  70°  C  (149°  to  158°  F).  Paper 
will  stand  a  temperature  of  90°  C  (194°  F),  but  it  is  neither  desirable 
nor  economical  to  allow  such  a  temperature  to  be  reached.  The 
following  table  is  of  interest  in  connection  with  underground 
cables.  The  dimensions  here  given  are  only  general. 

TABLE  VIII. 
Typical  Cable  Construction. 


Cables. 

No.  of  Conductors. 

Character 
of 
Conductor 

Sizes 
of 
Individual 
Wires. 

Electric  light  less  than  500  volts.  . 
Arc  lighting 

Single 
Single 

Stranded 
Solid 

No.  10  B.&S. 
or  smaller. 
No.  6  or  4 

High-tension  power  transmission  . 

Single,  concentric, 
duplex,  or  three 
conductors 

Stranded 

B.&S. 
No.  10  B.&S. 
or  smaller. 

Thickness  of  Insulation. 


Rubber. 

Saturated 
Fiber. 

Saturated 
Paper. 

Dry 

Paper. 

Thickness 
of  Lead. 

Electric  light  less  than  500 
volts  

Inch. 
A 

Inch, 
i 

Inch. 
JU 

Inch. 

A 

Inch. 

Tff  t0  TO 

Arc  lighting  

A-  to  A- 

% 

2 

High-tension    power    trans- 
,     mission  

-A  to  A 

H 
Tl¥ 

H 
31 

H 

»¥ 

10 

Selection  of  Voltage  to  be  Used.  The  voltage  to  be  selected 
for  a  given  system  depends  on  the  distance  the  power  is  to  be 
transmitted  as  well  as  its  amount,  and  on  the  use  to  be  made  of 
the  power.  If  a  lighting  load  is  concentrated  in  a  small  district, 
a  '2'20- volt  three-wire  system  will  give  very  good  service.  If  the 


POWEK   TRANSMISSION  73 


region  is  a  little  more  extended,  possibly  a  44:0 -volt  three-wire 
system  using  220-volt  lamps  would  serve  the  purpose  without  an 
excessive  loss  of  power  or  a  prohibitive  outlay  for  copper.  For 
location  when  the  service  is  scattered,  a  distribution  at  from  2,200 
to  4,000  volts  alternating  current  is  used,  transformers  being 
located  as  required  for  stepping  down  the  voltage  for  the  units 
which  may  be  fed  from  a  two-  or  three- wire  secondary  system. 

2,300  volts  (alternating)  is  a  standard  voltage  for  lighting 
purposes  and  for  polyphase  systems;  2,300  volts  is  often  taken  as 
the  voltage  between  the  outside  wires  and  the  neutral  wire  of  a 
four-wire  three-phase  distribution. 

For  railway  work,  550  to  600  volts  direct  current  is  used  up 
to  distances  of  about  5  or  6  miles,  beyond  which  it  becomes  more 
economical  to  install  an  alternating-current  main  station  and  sup- 
ply the  line  at  intervals  from  substations  to  which  the  power  is 
transmitted  at  voltages  of  from  6,600  to  30,000  or  even  higher, 
depending  on  the  distance  it  is  to  be  transmitted.  At  present, 
the  highest  voltage  used  in  long-distance  transmission  is  60,000, 
though  higher  values  are  contemplated.  Such  voltages  are  used 
only  on  very  long  lines,  and  each  one  becomes  a  special  problem. 
It  is  always  well  to  select  a  voltage  for  apparatus  which  may  be 
considered  as  standard  by  manufacturing  companies,  as  standard 
apparatus  may  always  be  purchased  more  cheaply  and  furnished 
in  shorter  time  than  special  machinery. 

Protection  of  Circuits.  Lightning  arresters  are  installed  at 
intervals  along  overhead  lines  for  the  protection  of  connected 
apparatus.  For  ordinary  lighting  circuits,  such  arresters  are  in- 
stalled for  the  protection  of  transformers,  and  are  located  preferably 
on  the  first  pole  away  from  the  one  on  which  the  transformer  is 
installed.  Care  should  be  taken  to  see  that  there  are  no  sharp 
bends  or  turns  in  the  ground  wire  and  that  there  is  a  good  ground 
connection.  For  the  high-tension  lines,  lightning  arresters  at 
either  end  of  the  circuit  are  relied  on  to  afford  the  greater  part  of 
the  protection.  In  some  localities,  a  wire  strung  on  the  same  pole 
line  at  a  short  distance  from  the  power  wires  and  grounded  at  very 
frequent  intervals  has  been  found  to  reduce  troubles  due  to  lightning. 

The  grounding  of  the  neutral  of  three-wire  secondary  systems 
forms  a  means  of  protection  of  such  circuits  against  high  potentials 


74  POWER  TRANSMISSION 


which  might  arise  from  accidental  contact  with  the  primaries,  and 
is  recommended  in  some  cases.  The  grounding  of  the  neutral  of 
high-tension  systems  reduces  the  potential  between  the  lines  and 
the  ground,  but  a  single  ground  will  cause  a  short-circuit  on  the 
line  with  any  grounded  system.  Grounding,  through  a  resistance 
which  will  limit  the  flow  of  current  in  such  a  short-circuit,  has 
been  recommended  and  is  employed  in  some  instances.  Spark 
arresters  are  installed  at  the  ends  of  high-tension  underground 
systems  to  prevent  high  voltages  which  might  injure  the  insulation 
in  case  of  sudden  changes  in  load,  grounds,  and  short-circuits. 


INDEX 


Part  I — POWEH  STATIONS;  Part  //— POWKK  TRANSMISSION 

Part  Page 

All-day  efficiency II,  -44 

Alternating-current  line  calculation II,  29 

examples  of II,  39 

Alternating-current  systems  of  distribution II,  21 

Annunciator  wire II,  9 

Boiler  efficiencies,  table I,  13 

Boiler  foundations I,  22 

Boilers I,  1() 

Cornish I,  11 

economic I,  12 

Lancashire I,  11 

marine I,  11 

multitubular I,  11 

water-tube I,  11 

Boilers,  firing  of '. I,  23 

Cable,  standard,  table I,  47 

Cable  construction,  table II,  72 

Cables II,  70 

Capacity  of  conductors  for  carrying  current II,  7 

Capacity  ratios,  table I,  61 

Central  station I,  3 

Charging  for  power,  methods  of I,  75 

Circuits,  protection  of II,  73 

Conductors II,  3 

capacity  of  for  carrying  current. II,  7 

for  various  conditions,  table. . II,  7 

Copper  losses : II,  44 

Copper  wire  table II,  4 

Cornish  boilers I,  11 

Cross-arms II,  56 

Curtis  turbine , : . .  . .  I,  27 

Direct-current  feeder  panels I,  50 

Distribution  systems II,  11 

multiple-series 

parallel 

series II,  H 

series-multiple II,  17 


II  INDEX 


Part  Page 
Draft 

mechanical I,  23 

natural ,  .  . I,  23 

Earthenware  conduits II,  67 

Economic  boiler I,  12 

Efficiency  of  transformer II,  44 

Electric  distribution  of  power II,  3 

Electrical  plant I,  36 

Engines,  gas , I,  34 

Exciter  panels I,  50 

Exciters I,  39 

Feed  water I,  20 

Feeding  appliances I,  20 

Feeding  point II,  15 

Firing  of  boilers. I,  23 

Formula,  general  wiring II,  30 

Frequency,  choice  of II,  49 

Fuel,  handling  of. I,  23 

Full  load  ratios,  table I,  61 

Galloway  boiler I,  11 

Gas  engines. I,  34 

Generating  station,  location  of.. I,  4 

Generator  efficiencies,  table. . I,  38 

Generators " I,  36 

Governors I,  34 

Gutta  percha.. II,  10 

Handling  of  fuel I,  23 

Hydraulic  plants I,  29 

Increase  in  boiler  efficiency,  table I,  20 

India  rubber it,  10 

Inductance II,  27 

per  mile  of  circuit,  table II,  26 

Insulation • II,  8 

Insulators II,  57 

Iron  or  core  losses.... II,  44 

Lancashire  boilers , I,  11 

Location  of  generating  station. I,  4 

Loss  of  power  in  steam  pipes I,  19 

Loss  in  pressure  in  steam  pipes,  formula  for I,  18 

Manholes II,  68 

Marine  boilers •  •  •  •  I,  11 

Matthiessen's  standard • •  •  •  •  II,  6 

Mechanical  draft I,  23 

Mechanical  strength  of  different  materials... II,  6 

Multiple-series  system  of  distribution II,  17 

Multiple  wire  system II,  18 

parallel....  II,  21 

polyphase II,  22 


INDEX  111 


Part  Page 
Multiple  wire  system 

series n ,  21 

three-wire 1 1 ,  i  # 

Multitubular  boiler I,  n 

Mutual  inductance H,  28 

Natural  draft I,  23 

Oil-cooled  transformer? I,  41 

Oil  switches I,  52 

Overhead  lines II,  50 

cross-arms II,  56 

insulators : II.  57 

location  of II,  51 

pins II,  59 

stresses  sustained  by II,  60 

supports  for.. II,  52 

Panels 

direct-current I,  50 

exciter I,  50 

total  output I,  51 

Parallel  systems  of  distribution II,  13,  21 

voltage  regulation  of II,  20 

Power  factor.... II,  33 

Power  station  buildings.. I,  63 

Pressure  of  water,  table I,  31 

Plant,  size  of I,  8 

Pump  log  conduit II,  66 

Regulation  of  a  transformer II,  45 

Resistance,  effects  of II,  7 

Resistance  of  electrical  conductors II,  4 

Riveted  hydraulic  pipe,  table I,  32 

Safety  devices I,  57 

Selection  of  system I,  6 

Series  system  of  distribution •. II,  11 

Series-multiple  system  of  distribution. '. II,  17 

Size  of  plant I,  8 

Station  arrangement I,  68 

Station  records I,  70 

Steam  engines I,  25 

Steam  piping I,  13 

arrangement I,  14 

material  for I,  10 

Steam  plant I,  10 

Steam  turbines I,  25 

Storage  batteries I,  44 

Stresses  sustained  by  pole  line •  •  •  •  II,  60 

Substations. . . '. I,  59 

Superheated  steam •  •  •  I,  19 

Switchboards I,  44 


II  INDEX 


Part  Page 
Draft 

mechanical I,  23 

natural I,  23 

Earthenware  conduits II,  67 

Economic  boiler I,  12 

Efficiency  of  transformer.. II,  44 

Electric  distribution  of  power II,  3 

Electrical  plant I,  36 

Engines,  gas ,  . I,  34 

Exciter  panels I,  50 

Exciters I,  39 

Feed  water I,  20 

Feeding  appliances I,  20 

Feeding  point II,  15 

Firing  of  boilers I,  23 

Formula,  general  wiring II,  30 

Frequency,  choice  of II,  49 

Fuel,  handling  of I,  23 

Full  load  ratios,  table I,  61 

Galloway  boiler I,  11 

Gas  engines .  I,  34 

Generating  station,  location  of.. I,  4 

Generator  efficiencies,  table I,  38 

Generators I,  36 

Governors I,  34 

Gutta  percha II,  10 

Handling  of  fuel I,  23 

Hydraulic  plants I,  29 

Increase  in  boiler  efficiency,  table I,  20 

India  rubber it,  10 

Inductance II,  27 

per  mile  of  circuit,  table II,  26 

Insulation. •• II,  8 

Insulators II,  57 

Iron  or  core  losses.... II,  44 

Lancashire  boilers I,  11 

Location  of  generating  station. I,  4 

Loss  of  power  in  steam  pipes I,  19 

Loss  in  pressure  in  steam  pipes,  formula  for I,  18 

Manholes • II,  68 

Marine  boilers •  •  •  •  I,  11 

Matthiessen's  standard •  •  •  •  II,  6 

Mechanical  draft I,  23 

Mechanical  strength  of  different  materials... II,  6 

Multiple-series  system  of  distribution II,  17 

Multiple  wire  system II,  18 

parallel....  II,  21 

polyphase II,  22 


INDKX  111 


Part  I'iitfe 

Multiple  wire  system 

series n,  21 

three-wire II,  is 

Multitubular  boiler I?  n 

Mutual  inductance. II,  28 

Xatural  draft I,  23 

Oil-cooled  transformers I,  41 

Oil  switches I,  52 

Overhead  lines II,  50 

cross-arms II,  50 

insulators .' II.  57 

location  of II,  51 

pins II,  59 

stresses  sustained  by II,  60 

supports  for.. II,  52 

Panels 

direct-current I,  50 

exciter I,  50 

total  output I,  51 

Parallel  systems  of  distribution II,  13,  21 

voltage  regulation  of II,  20 

Power  factor II,  33 

Power  station  buildings.. I,  63 

Pressure  of  water,  table I,  31 

Plant,  size  of I,  8 

Pump  log  conduit II,  66 

Regulation  of  a  transformer II,  45 

Resistance,  effects  of II,  7 

Resistance  of  electrical  conductors II,  4 

Riveted  hydraulic  pipe,  table. I,  32 

Safety  devices I,  57 

Selection  of  system I,  6 

Series  system  of  distribution •. II,  11 

Series-multiple  system  of  distribution '. II,  17 

Size  of  plant .  I,  8 

Station  arrangement. I,  68 

Station  records I,  70 

Steam  engines I,  25 

Steam  piping I,  13 

arrangement. I,  14 

material  for I,  16 

Steam  plant I,  10 

Steam  turbines I,  25 

Storage  batteries I,  44 

Stresses  sustained  by  pole  line •  •  •  •  II,  60 

Substations. . . '. I,  59 

Superheated  steam I,  19 

Switchboards I,  44 


IV  INDEX 


Part  Page 

System,  selection  of I,  6 

Tables 

boiler  efficiencies I,  13 

boiler  efficiency,  increase  in I,  20 

boilers,  floor  space  for , I,  12 

cable,  standard I,  47 

cable  construction II,  72 

capacity  in  Micro-Farads  per  mi.    of    circuit  for  three  phase 

system II,  25 

capacity  ratios I,  61 

conductors  for  various  conditions II,  7 

conductors  for  various  positions.... II,  8 

copper  wire II,  4 

exciters  for  single-phase  A.  C.  generators I,  39 

full  load  ratios I,  61 

generator  efficiencies. I,  38 

horse-power  per  cu.  ft.  of  water  per  m in.  for  different  heads.. .  .  I,  34 

inductance  per  mile  of  circuit. II,  26 

permissible  overload  33  per  cent I,  9 

rate  of  flow  of  water,  in  ft.  per  min.,  per  pipes  of  various  sizes.  .1,  22 

resistances  of  pure  aluminum  wire II,  5 

riveted  hydraulic  pipe I,  32 

temperature  effects  in  spans II,  62 

transmission  line  calculation II,  31 

water,  pressure  of I,  31 

wire,  standard I,  47 

Temperature  coefficient.. II,  6 

Three-wire  system  of  distribution II,  18 

Total  output  panels I,  51 

Transformer  connections II,  46 

Transformer  regulation II,  45 

Transformers I,  40;  II,  43 

efficiency  of II,  44 

oil-cooled • I,  41 

water-cooled I,  42 

Transmission  lines. • II,  24 

capacity...  •• II,  24 

Turbines I,  25 

Curtis.. I,  27 

steam I>  25 

water • I,  30 

Underground  construction II,  63 

Crompton  system II,  65 

Edison  tube  system II,  63 

Siemens-Halske  system II,  65 

French  system II,  65 

Underwriter's  wire II, 

Variation  in  voltage • II,  17 


INDEX 


Part  Page 

Voltage,  selection  of II,  72 

Voltage  regulation  of  parallel  systems II,  20 

Water-cooled  transformers I,  42 

Water-tube  boilers I,  11 

Water  turbines I,  30 

Weatherproof  wire II,  9 

Weight  of  materials. II,  (5 

Wire,  standard,  table I,  47 

Wiring  formula.... II,  30 


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